René Descartes's Natural Philosophy and Particular Bodies 9783031486630

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Studies in History and Philosophy of Science  60

Fabrizio Baldassarri

René Descartes’s Natural Philosophy and Particular Bodies

Studies in History and Philosophy of Science Volume 60

Series Editor Charles T. Wolfe, Département de philosophie & ERRAPHIS, Université de Toulouse Jean-Jaurès, Toulouse, France Editorial Board Members Catherine Abou-Nemeh, School of History, Philosophy, Political Science, Victoria University of Wellington, Wellington, New Zealand Rachel A. Ankeny, University of Adelaide, Adelaide, SA, Australia Peter Anstey, School of Humanities, University of Sydney, Sydney, NSW, Australia Delphine Bellis, Paul Valéry University, Montpellier, France Meyssa Ben Saad, Université de la Manouba, Manouba, Tunisia Hourya Bentouhami, University of Toulouse, Toulouse, France Antonio Clericuzio, Roma Tre University, Roma, Italy Sophia M. Connell, Birkbeck, University of London, London, UK Matthew Daniel Eddy, Durham University, Durham, UK Nicholas Dew, McGill University, Montreal, Canada Steven French, Department of Philosophy, University of Leeds, Leeds, UK Ofer Gal, Unit for History and Philosophy of Science, University of Sydney, Sydney, Australia Laura Georgescu, University of Groningen, Groningen, The Netherlands Thierry Hoquet, Université Paris Nanterre, Nanterre, France Clemency Montelle, School of Mathematics & Statistics, University of Canterbury, Christchurch, New Zealand Pietro Daniel Omodeo, Ca’ Foscari University of Venice, Venice, Italy Carla Rita Palmerino, Radboud University, Nijmegen, The Netherlands Lydia Patton, Virginia Tech, Virginia, USA Nicholas Rasmussen, UNSW Sydney, Kensington, Australia Jonathan Regier, Ca’ Foscari University of Venice, Venice, Italy Anne-Lise Rey, Université Paris Nanterre, Nanterre, France Sophie Roux, République des savoirs, École Normale Supérieure - PSL, Paris, France C. J. Schilt, Vrije Universiteit Brussel, Brussels, Belgium John Schuster, University of New South Wales Sydney, Kensington, Australia Suman Seth, Cornell University, New York, USA Tzuchien Tho, University of Bristol, Bristol, UK Koen Vermeir, SPHERE UMR 7219, Centre National de la Recherche Scientifique, Paris, Paris, France Angela Willey, University of Massachusetts Amherst, Amherst, USA Richard Yeo, Griffith University, Brisbane, Australia Anna C. Zielinska, Département de Philosophie, Université de Lorraine & Archives Henri Poincaré, Nancy, France

Studies in History and Philosophy of Science is a peer-reviewed book series, dedicated to the history of science and historically informed philosophy of science. The series publishes original scholarship in various related areas, including new directions in epistemology and the history of knowledge within global and colonial contexts. It includes monographs, edited collections, and translations of primary sources in the English language. These cover a broad temporal spectrum, from antiquity to modernity, and all regions of the world.

Fabrizio Baldassarri

René Descartes’s Natural Philosophy and Particular Bodies

Fabrizio Baldassarri Department of Philosophy and Cultural Heritage Ca’ Foscari University of Venice Venice, Italy

ISSN 1871-7381 ISSN 2215-1958 (electronic) Studies in History and Philosophy of Science ISBN 978-3-031-48662-3 ISBN 978-3-031-48663-0 (eBook) https://doi.org/10.1007/978-3-031-48663-0 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.

Acknowledgments

This book is a substantial re-elaboration of my PhD dissertation that I defended at the Università di Parma in 2013. Chapters 2, 3, and 6 are entirely new, and Chaps. 4 and 5 have been substantially and painstakingly re-worked, while the underlying idea of my PhD dissertation remains. In this sense, I owe a lot to the post-doctoral fellowships I held and the researches I pursued in the years after my doctoral training. I must thank the institutions who supported my research, namely, the Institute for Research in the Humanities (IRH) of the University of Bucharest (Romania), the DAAD, the IRS grant I held at Bar-Ilan University, the Kristeller-Popkin Fellowship of the Journal of the History of Philosophy, the postdoctoral fellowship at Herzog August Bibliothek in Wolfenbüttel, the postdoctoral fellowship of the CNSC-UEFSCIDI of Romanian government, and the Marie Skłodowska-Curie Individual Fellowship I held at Ca’ Foscari University of Venice and Indiana University, Bloomington. I am grateful to the supervisors who have encouraged me throughout the years, namely, Vlad Alexandrescu, Domenico Bertoloni Meli, Martin Mulsow, Ohad Nachtomy, and Marco Sgarbi. A number of friends and colleagues have offered serious advice and support in many ways. I wish to thank Igor Agostini, Justin Begley, Simone D’Agostino, Benjamin Goldberg, Simone Guidi, Helen Hattab, Francesco Luzzini, Oana Matei, Evan Ragland, and Philip Sloan, who have read several chapters of the book. I also thank the anonymous referees, who have carefully read previous versions of my manuscript, providing me with some important insight to make it more clear and consistent. I have also discussed sections of this book with Monica Azzolini, Florike Egmond, and Iolanda Ventura. Their comments, remarks, suggestions, friendship, and constant help have been important to complete this enterprise, while all mistakes and imprecisions are entirely my fault. A special thank goes to Theo Verbeek, who has been the safe haven in my exploration of Descartes’s philosophy and science, and his expertise and knowledge have meant for me something that I will never be able to return. I wish to express my gratitude to the staff of the Biblioteca di Filosofia of the University of Bologna, the Forchunsbibliothek Gotha, the Herzog August Bibliothek Wolfenbüttel, the Library of Lyon Diderot at the ENS Lyon, the Centro v

vi

Acknowledgments

Dipartimentale di studi su Descartes Ettore Lojacono of the University of Salento, the Universiteitsbibliotheek Uithof at Utrecht University, the Leiden University Library, the Library at the Max Planck Institute for the History of Science in Berlin, the Library at the Warburg Institute, the Whipple Library at Cambridge University, the Firestone Library at Princeton University, the BAUM at Ca’ Foscari University of Venice, and the Lilly Library at Indiana University Bloomington. This book builds on and substantially expands a number of essays I have published in the past years, and I have importantly benefitted from all reviewers and editors who have commented my work. While it is impossible to recall all meetings, seminars, and conferences I attended throughout the years, in a few occasions I have specifically discussed the topic now published in these chapters. In various order, these are: a lecture to the students at Università Cattolica del Sacro Cuore, in Milan, organized by Elena Rapetti; a lecture at a conference at the University of Basel organized by Dominique Brancher and Jean-Claude Monferran; a seminar organized by Antonio Clericuzio at the University of RomaTre; an event organized by Cinzia Ferrini at the University of Trieste on curiosities and wunderkammern. More recently, I have presented chapters of my book at the Houston University Seminar Circle in Philosophy, in which I discussed Chap. 3 on nature, organized by Helen Hattab; the Seminar in History and Philosophy of Science at the University of Notre Dame, in which I discussed Chap. 6 on animals, organized by Evan Ragland; a lecture at the graduate students’ seminar on early modern philosophy at Princeton University, organized by Daniel Garber, in which I presented Chap. 5 on plants; and the Cabinets of Natural History of Cambridge University, organized by Silvia Maria Marchiori, in which I discussed Descartes’s natural history at large. I am truly grateful to all organizers and participants for their very helpful comments and remarks, and for their willingness to discuss my work at length. Last but not least, a great thanks goes to my family, my mother and my father, who have always supported me in all these years, and especially to my wife, Ilaria Carrino, who patiently and unshakably stands at my side—together with Febe Lucia, they have always showed me home and where I belong, while I have been travelling too much around the world. Thank you! Paris, March 2023

Fabrizio Baldassarri

Contents

1

2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 A Tension in Descartes’s Program: The Case of Particular or Individual Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 The Gaps in Descartes’s Study of Nature . . . . . . . . . . . . . . . . . . . 1.3 . . . and in Its Scholarship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 The Aim of This Book: Descartes’s History of Nature and Its Open Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 The Matter of This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 The End of History and a New Scientia . . . . . . . . . . . . . . . . . . . . 2.1.1 Against History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2 Descartes’s Scientia and His Method . . . . . . . . . . . . . . . . . 2.2 A Method of Experiments: The Regulae and the Correspondence of the Early 1630s . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Experiments and Method in Descartes’s Epistemology . . . . 2.2.2 Reason and Experience in the Correspondence with Beeckman: A Battle for Scientia . . . . . . . . . . . . . . . . . . . . 2.2.3 Mersenne and Descartes: Lists of Qualities, Useful Experiments, and Natural History . . . . . . . . . . . . . . . . . . . 2.3 Observations in a System: Knowledge of Particular Bodies from the Discours to the Principia . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Method and Necessary Experiments . . . . . . . . . . . . . . . . . 2.3.2 A Priori and A Posteriori: Method and Experiment in the 1638 Correspondence . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 A History of Natural Particulars in the Principia . . . . . . . . . 2.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 4 8 11 12 15 19 22 22 25 29 29 34 37 41 41 44 46 49

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3

4

5

Contents

Nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 A Theoretical Model: The World Imagined . . . . . . . . . . . . . . . . . 3.2 Constructing Nature: A Mechanical World . . . . . . . . . . . . . . . . . . 3.2.1 Rules of Nature and Elements in Le Monde . . . . . . . . . . . . 3.2.2 The Mechanization of Material Objects: The Principia, Part 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Describing Natural Particulars: The Visible World . . . . . . . . . . . . 3.3.1 Observation in Le Monde . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Les Météores and the Rainbow . . . . . . . . . . . . . . . . . . . . . 3.3.3 A History of Natural Phenomena: Observed Nature in the Principia . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 The Rejection of Alchemy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Between Wonder and Observations: The Bologna Stone and Other Curious Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 The Qualities of Particular Bodies and Salt in the 1630s . . . . . . . . 4.3.1 The Qualities of Bodies in Le Monde . . . . . . . . . . . . . . . . 4.3.2 Salt in Descartes’s Philosophy . . . . . . . . . . . . . . . . . . . . . 4.4 A Philosophy of Natural Bodies: The Generation of Mercury, Salt, Oily Natures, Minerals, and Metals . . . . . . . . . . . . . . . . . . . 4.4.1 A Short History of Minerals . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 The Earth as a Chymical Laboratory . . . . . . . . . . . . . . . . . 4.5 The Magnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Magnetism Before the Principia . . . . . . . . . . . . . . . . . . . . 4.5.2 Screw-Shaped Particles in Descartes . . . . . . . . . . . . . . . . . 4.5.3 The Magnet in the Principia . . . . . . . . . . . . . . . . . . . . . . . 4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Classifying Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Plants and Animals: Mechanical Analogies and the Vegetative Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2 A Mechanical Gradation Between Plants and Animals . . . . 5.2 Descartes and the Dutch: Corpuscles, Catalogs, Observations, and Botanical Gardens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Isaac Beeckman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Huygens and Brosterhuysen . . . . . . . . . . . . . . . . . . . . . . . 5.2.3 Circulating Seeds and Catalogs . . . . . . . . . . . . . . . . . . . . . 5.2.4 Henricus Reneri . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 The Mechanical Physiology of Plants . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Plant Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Plant Nutrition and Growth . . . . . . . . . . . . . . . . . . . . . . . 5.3.3 Grafting, Cultivating, and the Flavors of Plants . . . . . . . . . 5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51 53 57 57 60 63 64 65 71 72 75 78 82 88 88 90 96 96 97 104 104 110 112 115 117 121 121 125 127 127 130 133 134 137 138 142 145 149

Contents

6

7

Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Automata and Animal Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 History of Animals: Movements, Instincts, Spirits, and Animal Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 A Mechanical Scale of Animals: Brutes, Dogs, Cows, Fish, Birds, and Oysters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 The Mechanical Life of Animals . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ix

153 157 162 168 178 183

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary Sources: René Descartes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary Sources: Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

189 189 190 191

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

Abbreviations

AT

CSM

CSMK

G MM

Shapiro

Adam, Charles and Tannery, Paul (eds.) 1897–1913. René Descartes. Œuvres, 13 vols. Paris: Léopold Cerf. Nouvelle présentation par J. Beaude, P. Constable, A. Gabbey et B. Rochot, 11 vols. Paris: Vrin, 1964–1974. Cottingham, John, Stoothoff, Robert and Murdoch, Dugald (eds.) 1984. The Philosophical Writings of Descartes, 2 vols, edited and translated. Cambridge-New York-Port Chester-Melbourne-Sydney: Cambridge University Press. Cottingham, John, Stoothoff, Robert, Murdoch, Dugald and Kenny, Anthony (eds.) 1991. The Philosophical Writings of Descartes, vol. III The Correspondence, edited and translated. Cambridge-New York-Port Chester-Melbourne-Sydney: Cambridge University Press. Gaukroger, Stephen (ed.) 1998. René Descartes, The World and Other Writings, ed. and transl. Cambridge: Cambridge University Press. Miller, Valentine Rodger, and Miller Reese P (eds.) 1982. René Descartes, Principles of Philosophy, translated, with explanatory notes. Dordrecht, Boston, and London: Kluwer. Shapiro, Lisa (ed.) 2006. The Correspondence between Princess Elisabeth of Bohemia and René Descartes, edited and translated. Chicago: The University of Chicago Press.

xi

List of Figures

Fig. 1.1 Fig. 3.1 Fig. 3.2 Fig. 3.3 Fig. 4.1

Fig. 4.2 Fig. 4.3

Fig. 4.4 Fig. 5.1 Fig. 5.2 Fig. 5.3

Fig. 5.4

Snowflakes with various figures. In René Descartes, Les Météores, VI, AT VI 302 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nature and meteorological phenomena. In René Descartes, Les Météores, II, AT VI 242 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Observing the rainbow from a fountain. In Les Météores, VIII, AT VI 344 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Observing the rainbow from a globe of water made by a flask. In Les Météores, VIII, AT VI 326 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How fire is struck from flints: flint A has globules of air, flint B is struck and particles are removed, as shown in flint C, when fires develop. In René Descartes, Principia philosophiae, IV, art. 84, AT VIII-1 251 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The needle ACBD, with the pores directed from B to A, in Descartes to Huygens, May 24, 1643, AT III 817 . . . . . . . . . . . . . . . . On the left, the globules within which particles enter and take a screw-shaped form; on the right, screw-shaped particles. In Henricus Regius, Fundamenta physices, chap. II, 53 . . . . . . . . . . . . The flowing of screw-shaped particles in the Earth and around it. In Principia, AT VIII-1 288 . . . . . . . . . . . . . . . . . . . . . . . . . . Heliotropic clock. In Athanasius Kircher, Magnes sive de arte magnetica, Rome 1654, 508 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The formation of fires in stored hay. In René Descartes, Principia philosophiae, IV, art. 92, AT VIII 256 .. . . .. . . .. . . . .. . . .. . The movements of particles in the formation of animal (on the left) and vegetal bodies (on the right). In René Descartes, Primae Cogitationes circa generationem animalium, AT XI 534 . .. . . . . . . . . .. . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . .. . . . . The formation of plants. In René Descartes, Excerpta anatomica, Appendix, AT XI, unpaged, Fig. XXII . . . . . . . . . . . . . . . . .

3 67 69 70

100 109

111 113 119 119

139 140 xiii

xiv

List of Figures

Fig. 5.5

Author’s representation of the motions of particles, from Baldassarri 2019: 53 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

Fig. 6.1

A dissected sheep drawn by Descartes. In René Descartes Excerpta anatomica, Appendix, AT XI, unpaged, Fig. XI . . . . . . . . . The representation of the cod intestines. In René Descartes, Exerpta anatomica, Appendix, AT XI, unpaged, Fig. XVIII . . . . . . . The representation of a hole that replaces nostrils in the cod. In René Descartes, Excerpta anatomica, Appendix, AT XI, unpaged, Fig. XXI .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . The illustration of a dog dissection to inspect the organs of the abdomen. In Henricus Regius, Fundamenta physices, cap. X, 171 . . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . The unity of organs in the living body. In René Descartes, L’Homme, AT XI 128 .. . . .. . . .. . . . .. . . .. . . .. . . .. . . . .. . . .. . . .. . . .. . . . .. .

Fig. 6.2 Fig. 6.3

Fig. 6.4

Fig. 6.5

163 170

171

175 179

Descartes composing his system of the world, engraving from A.L.F. Sergent, Portraits des grands hommes, femmes illustres et sujets mémorables de France. Paris: Blin, 1786-1792, ill. 52. [Source: gallica.fr / BNF] http://catalogue.bnf.fr/ark:/12148/cb40355179s

Chapter 1

Introduction

essendo che all’istorico appartiene il solo effetto, ma la ragione è officio del filosofo [Galileo, Il Saggiatore, 46, 8] Cognitio hominis de rebus naturalibus, tantum per similitudinem eorum quae sub sensum cadunt: et quidem eum verius philosophatum arbitramur, qui res quaesitas felicius assimilare poterit sensu cognitis. [Cogitationes privatae, AT X 218–219]

On the morning of Monday, February 5, 1635, René Descartes stepped into the street in Amsterdam to observe phenomena in the sky. He reported this experience in a notebook, today collected under the title Problemata, a section of Excerpta anatomica, and published in volume 11 of the Œuvres de Descartes edited by Charles Adam and Paul Tannery. This is the text: 5 February 1635. While the Northeast wind blew, as it had snowed the day before and there was what we call verglas [black ice]. Still, there were a few tiny flakes of this size (H), as to their figure resembling the crystalline humor, and transparent. I noted that some of them had 6 very short rays [points as of a star], pale, almost white, which were bigger than the flake. I say that on February 5 I noted a great variety of small stars of snow: First, several solid hexagons like this (K), very transparent, smooth and tiny, of a different size; Then, a few rounds like this (Q) [. . .] Then, others without a center, and a little bigger than the previous one, and with rays like a lily; And then some small rods, not bigger than a small needle [. . .] with at the two ends a small star like this (F) [. . .]. And then with twelve rays [or points] sometimes equal, sometimes not. And I also saw one [star] on a ray, where there was a column with another star, but smaller. And four or five made of 8 rays, 4 shorter that the other, and one could see that they were made like this, like (E) (Excerpta anatomica, AT XI 626–627 [translation is mine])1

Original Latin is: “5a Feb. 1635. Caecia flante, cum praecedenti die etiam ninxisset, et id quod vocamus verglas cecidisset, erant autem granula hujus magnitudinis (H ), humorem cristallinum figura referentia, et pellucida; et uni et alteri ex quibus notavi sex radios brevissimos et ex albo

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© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 F. Baldassarri, René Descartes’s Natural Philosophy and Particular Bodies, Studies in History and Philosophy of Science 60, https://doi.org/10.1007/978-3-031-48663-0_1

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Introduction

A year later, he substantially reorganized these notes in a text that was to be published in June 1637. The latter composes a section of Discourse 6 of Les Météores,2 one of the essays of the Discours de la Méthode (1637), to which Descartes added a few figures representing different flakes of snow (see Fig. 1.1)—a few figures of snowflakes are also included in the appendix of Excerpta anatomica, but these are unintelligible. The observation of snowflakes contains several innovative features and is paradigmatic of Descartes’s enterprise.3 As Han van Ruler has highlighted, this reveals more than the philosopher’s mere “eagerness to seize the opportunity and study what was falling down from the clouds” (Van Ruler 2019: 4) as the study of snow would put him in line with the scholars of his time.4 More importantly, it uncovers a crucial aspect of Descartes’s attempt to practice a new way of looking at nature. Let us list these features. First, Descartes did not content himself with what he read in books about particular phenomena but observed them in nature. Second, he made an inventory of various snowflakes he observed, more or less like a Baconian natural history.5 Third, he analyzed the details of these bodies into elements, following mathematical reasoning. The perceptual difference in figuration follows a geometrical order. The observation of a singular natural phenomenon (snow) resulting in an inventory of individual forms (for instance, hexagonal snowflakes) can ultimately be seen as an attempt to apply a theoretical framework to the knowledge of nature and to provide a systematization of nature and its diverse bodies in terms of a geometrical and mechanical model. In this sense, this knowledge focuses on the causes producing such bodies, not on the mere

pallidos, etiam crassitiem granuli superantes: 5a, inquam, Feb. notavi valde varias nivis stellulas: primo, quaedam solida hexagona talia (K ), valde pellucida, polita et tenuia, inaequalium magnitudinum; deinde rotulas tales (Q), pulchriores quam arte fingi possint, etiam cum puncto albido minutissimo in centro, et fere totas pellucidas; deinde etiam alias sine puncto in centro, et paulo majores, cum radiis instar liliorum; ac deinde columnulas, crassitiem minutae aciculae aequantes, pellucidas, et ad utramque extremitatem habentes stellulam hoc modo (F); quasdam etiam habentes aliquid in medio sic (F). Non potui autem notare an quod in medio erat, esset hexagonum. Erant autem tam affabre factae, ut nihil magis. Paulatim vero ceciderant his breviores, in quarum una extremitate stella erat major, quam in altera; et postea duplices, cum 12 radiis interdum aequalibus, interdum non. Et unam vidi, cujus uni radio columna cum alia minore stellula insidebat. Et quatuor aut 5 ex octo radiis factas, ita ut quatuor essent aliis breviores, et appareret ex duabus factas esse sic (E). Erant autem omnes tota die satis spissae; sed sub vesperem, cum ningere desineret, erant multo tenuiores.” 2 Les Météores, VI, AT 298–308, and specifically 300–305; see also the Latin translation, Meteora, VI, AT VI 686–689. Several differences, however, surface between these texts and the one of the Excerpta anatomica, and while the note only reports on one morning of observations, the published text reports on several days. See also Frank 1974. One should note that Discourse 6 also discusses hailstorm, which is the subject of another note of the Excerpta, AT XI 623–624. See Descartes to Chanut, March 6, 1646, AT IV 377–376. 3 Snowflakes were a controversial topic in seventeenth-century knowledge, see, for instance, Glouberman 1995; Wragge-Morley 2020: 83–90. 4 See Kepler, Nive Sexangula; Gassendi 1964: vol. IV, 102–103. Cf. Gassendi to Mersenne, February 4, 1629, CM, vol. II, 196–199. Descartes to Mersenne, March 4, 1630, AT I 127. 5 I am not going to discuss the various meanings of natural history. See Smith 2022.

1

Introduction

3

Fig. 1.1 Snowflakes with various figures. In René Descartes, Les Météores, VI, AT VI 302

effects, ultimately operating for the entirety of nature. The case of snowflakes thus exemplifies Descartes’s attempt to connect the knowledge of “things” with theoretical philosophizing—the knowledge of causes—regulated by a geometricomechanical model working for nature as a whole.6 This is consistent with his scientific project of the late 1620s and early 1630s, when Descartes became interested in physics. In 1629, spurred by Henricus Reneri (1593–1639), Descartes examined the case of parhelia (or mock sun) that had occurred in Rome, and from this specific problem, he committed “to make a systematic study of the whole meteorological phenomena” (Descartes to Mersenne, October 8, 1629, AT I 23; CSMK 6)7 from which he moved on to engage with the whole of nature.8 His ultimate aim was to write an entire physics in a treatise he worked on in the early 1630s entitled Le Monde ou traité de la Lumière (left unfinished in 1633 and posthumously published in 1664). In his physics, he appeared little interested in particular, strange or rare bodies and did not collect their variety, a very common endeavor to deal with the whole of nature in premodern times, but reduced natural

6

Cf. Grafton and Siraisi 1999; Roberts et al. 2007; Smith et al. 2014. Cf. Descartes to Mersenne, November 13, 1629, AT I 70; CSMK 7: “Rather than explaining just one phenomenon I have decided to explain all the phenomena of nature, that is to say, the whole of physics.” Henricus Reneri had asked Descartes to provide an explanation of this phenomenon, after he received from Pierre Gassendi a copy of its description made by Jesuit Christoph Scheiner (1573/ 1575–1650). See Bellis 2012; Buning 2013: 174–176, 207. 8 In 1629 and 1630, Gassendi published his explanation of the phenomenon. See Gassendi, Phaenomenon; and Gassendi, Parhelia. In 1630, Scheiner published his text on the phenomenon. Cf. Scheiner, Rosa Ursina. See Taussig 2023. 7

4

1

Introduction

phenomena to a mathematical and mechanical model, therefore accounting for them in terms of motion, size, shape, and arrangement of particles, and by means of a geometrical figuration.9 This reduction characterizes Descartes’s mechanization of nature, and it applies—or should apply—to all individuals. Descartes’s commitment to physics in these mechanical terms appears consistent with his philosophical program, grounded on the claim that knowledge is an activity of thinking and belongs to reason. In his epistemology, Descartes argues that one should “place more trust in our reason than in our senses” (Principes de la philosophie, II, art. 52, AT IX-2 93; MM 69, n. 62), as “the intellect alone is capable of scientia” (Regulae ad directionem ingenii, IX, AT X 398; CSM I 32 [translation slightly modified]), i.e., certain and evident cognition of which “our minds seem capable” (Regulae, II, AT X 362; CSM I 10) while the senses—namely observations—are deceitful. Famously, in the Discours, he remarks that knowledge is like a chain of deductions originating in the principles that lie within our mind, like the chains of geometricians (Discours de la Méthode, VI, AT VI 63–64; CSM I 143–144) for mathematics alone provides knowledge with certainty.10 In this sense, Descartes conceived knowledge as mathematical demonstrations, that is, “a kind of philosophizing in which nothing is argued except what is mathematical and evident” (Descartes to Plempius for Fromondus, October 3, 1637, AT I 421), and this concerns physics as well, as seen for the case of snowflakes. However, a contrast arises between a demonstrative, universal science, whose unity belongs to the unity of the mind, and the knowledge of particular bodies, in which the observation of the diversity of nature is necessary. In Descartes’s natural philosophy, the traditional question of whether intellectual cognition is only of universals or can directly grasp individuals takes the shape of the application of the geometrico-mechanical identification of matter to particular things.11

1.1

A Tension in Descartes’s Program: The Case of Particular or Individual Bodies

A tension surfaces in the application of his rational epistemology to the diversity of nature and to individuals or particulars. In Aristotelian scientia, a similar issue involves the inference from the knowledge of universals to grasping the knowledge 9

The case of the rainbow clearly reveals this aspect, as brilliantly discussed by Daniel Garber. For a broad discussion of mechanical philosophy, see Gabbey 2004; Roux 2004. 10 I am not dealing with the important issue of the creation of eternal truth, but only glossing Descartes’s claim in the Discours in which he stressed his delight “in mathematics, because of the certainty and self-evidence of its reasonings” (Discours de la Méthode, I, AT VI 7; CSM I 114). See Bonicalzi 1990. 11 On Descartes’s natural philosophy, see Garber 1992: 181; Garber 2006; Anstey and Schuster 2013; and Schuster 2013. On grasping the knowledge of individuals, see Grosholz 1991; Garber 1992; Grosholz 1994; Ablondi and Barbone 1994; Des Chene 1996; Reid 2014; Toth 2022.

1.1

A Tension in Descartes’s Program: The Case of Particular or. . .

5

of natural particulars, as the attention to particular features would detract from the universal science of natural philosophy.12 Yet, a more specific puzzle concerns Descartes’s program. On the one hand, in his epistemology, knowledge consists of an intellectual systematization and takes the shape of a mathematical inference to which one should reduce the object of knowledge. In a March 1619 letter to Isaac Beeckman (1588–1637), Descartes envisages that his “completely new science [scientiam penitus novam] would provide a general solution of all possible equations involving any sort of quantity [. . .] each according to its nature” (Descartes to Beeckman, March 26, 1619, AT X 156–157; CSMK 2). In a November 1629 letter to Marin Mersenne (1588–1648), Descartes proclaims that “order is what is needed: all the thoughts which can come into the human mind must be arranged in an order like the natural order of the numbers” (Descartes to Mersenne, 20 November 1629, AT I 80; CSMK 12). In the Regulae ad directionem ingenii, he states that in order to know anything, one should “make a direct survey of the problem [. . .] intuiting, through a chain of sound reasonings, the dependence of one term on another” (Regulae ad directionem ingenii, XVII, AT X 459; CSM I 70). In the Discours, he irons out that his method operates similarly to the “long chains composed of very simple and easy reasonings, which geometricians customarily use to arrive at their most difficult demonstrations” (Discours de la Méthode, II, AT VI 19; CSM I 120). Grounded in the clarity and distinctness of intellectual ideas, scientific knowledge takes the shape of mathematical demonstrations that reduce nature to a geometricomechanical model—ultimately identifying naturalia and artificialia, nature and mechanics.13 On the other hand, while this reduction works for nature in general, grappling with particular bodies appears more problematic. Nature is indeed a diverse composition of various individuals, which cannot be easily reduced to a mathematical and mechanical format. Descartes himself addresses this issue in the Discours, where he claims that difficulties arise when: descending to more particular things, [because] I did not think the human mind could possibly distinguish the form or species of bodies that are on the earth [. . .]. Consequently, I thought the only way of making these bodies useful to us was to progress to the causes by way of the effects and to make use of many special observations” (Discours de la Méthode, VI, AT VI 64; CSM I 144).14

Still, both the claim to move from the effects back to causes and the appeal to observations are problematic within Descartes’s epistemology, as I later discuss in this book. Let us focus on this tension a bit more. 12 On the relationship between natural history and natural philosophy, see Blair 2006. Cf. Freedberg 2002. On the difficulties in grasping knowledge of individuals only indirectly in Aristotelian tradition, see Antognazza 2023. 13 Principia philosophiae IV, art. 203, AT VIII-1 326: “Atque ad hoc arte facta non parum me adjuverunt: nullum enim aliud, inter ipsa et corpora naturalia, discrimen agosco, nisi quod arte factorum operationes, ut plurimum, peraguntur instrumentis adeo magnis, ut sensu facile percipi possint: hoc enim requiritur, ut ab hominibus fabricari queant.” 14 On the scientific explanation of individuals in the seventeenth century, see Joy 2006: 73–76.

6

1

Introduction

One of the reasons for such a tension lies in Descartes’s philosophical program as a whole. From the intellectual certainty of the cogito, the ground of true knowledge, Descartes’s metaphysics of the two substances entails that “all corporeal nature [. . .] is the subject matter of pure mathematics” (Meditationes de prima philosophia, V, AT VII 71; CSM II 49), ultimately resulting in the mechanical commitment to reducing all bodies to particles with sizes, shapes, figures, and motions, following determinate (mechanical) rules.15 This reduction to a mathematical equation or to a mechanical quantification has a dramatic consequence, resulting in a gray ontology, as brilliantly pointed out by Jean-Luc Marion.16 Descartes’s mechanistic alternative to substantial forms and hylomorphism fuels the claim that all objects of knowledge should be stripped of all qualities, including individuality. Consistently, Descartes defines nature as extended matter, as the “extension, or the property it has to occupy space [is] not an accident, but its true form and its essence” (Le Monde, AT XI 36; CSM I 92), namely the only attribute of the body. In the Meditationes, Descartes expresses his view of the body as a geometrical object, which could be accounted for in mechanical terms alone.17 In the Discours, he claims that, in spite of the vastness of the powers of nature, “any particular effect [. . .] can be deduced from the principles” (Discours de la Méthode, VI, AT VI 64–65; CSM I 144), that are the mechanical rules of his physics. As Desmond Clarke has shown, “Descartes’ whole scientific project is one of imaginatively constructing descriptions of the motions of particles which might explain natural phenomena” (Clarke 1982: 124). In sum, from the definition of cognition as an activity of reason that operates by means of mathematical and mechanical models, Descartes captures the whole of nature by reducing it to the mechanical arrangement of identical particles—in this sense, nature is not a composition of individual bodies, but a mechanical combination of extended particles that follows some kinematic rules. Yet, Descartes was not content to restrict knowledge to the abstract entities of mathematics but extended his philosophical program to various disciplines, such as “the virtues of plants, the motions of stars, the transmutations of metals, and the objects of similar disciplines” (Regulae ad directionem ingenii, I, AT X 360; CSM I 9). Developing from the principles of his metaphysics and physics, he investigated all disciplines, as the metaphor of the tree of philosophy depicts.18 What relates all disciplines is the method, which brings unity to scientia as an intellectual cognition.19 In the Regulae, Descartes conceives the method as a mathesis universalis that 15 Regulae ad directionem ingenii XII, AT X 419; CSM I 45: “Those simple natures, on the other hand, which are recognized to be present only in bodies – such as shape, extension and motion, etc. – are purely material.” Cf. Garber 1992: 63–70. Garber 2001: 112. Hattab 2009. Ariew 2009: 111. A different reading is in Toth 2022: 935–936. 16 Marion 1981: 185–190. 17 Meditationes de prima philosophia, V, AT VII 63; CSM II 44: “I also enumerate various parts of the thing, and to these parts I assign various sizes, shapes, positions and local motions.” See also, Principia philosophiae, I, art. 48, AT VIII-1 22–23; CSM I 208–209. 18 Lettre-Préface, AT IX-2 14. 19 See Dika 2015.

1.1

A Tension in Descartes’s Program: The Case of Particular or. . .

7

helps encompass everything in the universe within the order of reason.20 Through his method, it is therefore possible to reduce the variety and complexity of singular bodies to the mechanical principles of his physics and, thus, to a geometrical pattern. Thus, his method paves a way to solve the tension described above and attempts to bridge the gap between his rational epistemology and the diversity and scattered condition of the particular bodies of nature. In the Regulae, Descartes provides examples of this application, as he fleshes out a way to explain external bodies through mathematical quantification. As he writes in Rule 14, “the real extension of bodies [. . .] should be pictured in our imagination entirely by means of bare figures” (Regulae ad directionem ingenii, XIV, AT X 438; CSM I 56) leaving aside external qualities, and dealing only with “familiar entities, such as extension, shape, motion and the like. The question whether a crown is made of silver or of gold makes no difference to the way we imagine its shape” (Regulae ad directionem ingenii, XIV, AT X 439; CSM I 57) and therefore to the way one knows it. Accordingly, scientific knowledge (scientia) thus consists of an abstraction from qualities and a reduction not to the substantial forms or to the universals of Scholastic tradition but to a mathematical proportion and a mechanical model through which one should visualize the object of knowledge. In this sense, any figuration or construction of forms results from a mechanical or mathematical representation—in the Regulae, Descartes specifies intellectual imagination as a power of conceiving images that helps in conceiving nature as a construction of magnitudes.21 In Rule 12, through the example of colors, he reduces perceived qualities to mathematical quantification. His geometrization of colors uncovers the ways in which “the infinite multiplicity of figures is sufficient for the expression of all the differences in perceptible things” (Regulae ad directionem ingenii, XII, AT X 413; CSM I 41). Accordingly, the mind reduces the information of particular bodies to spatial modifications regulated by mathematics and mechanical models—in a way that is consistent with his explanation of sensation as a pressure on human organs. Yet, the act of reducing bodies to a geometrical system made of shape, figure, and motion, i.e., the modes of extended matter, results in particular bodies losing their individuality in favor of the mechanical arrangement of particles. This opens out to doubts and problems, as the complexity of the interactions of particles in shaping bodies means that the actual formulation of mathematical description could be

Cf. Regulae ad directionem ingenii, IV, AT X 377–378; CSM I 19: “I came to see that the exclusive concern of mathematics is with questions of order or measure and it is irrelevant whether the measure in question involves numbers, shapes, stars, sounds, or any other object whatever.” See Crapulli 1969. 21 Regulae ad directionem ingenii, XII, AT X 416; CSM I 42: “when applying itself [i.e., the cognitive power] along with imagination to the ‘common’ sense, it is said to see, touch etc.; when addressing itself to the imagination alone, in so far as the latter is invested with various figures, it is said to remember; when applying itself to the imagination in order to form new figures, it is said to imagine or conceive; and lastly, when it acts on its own, it is said to understand.” On this point, see Sepper 2013: 287. See also Lüthy 2006; Bellis 2010. 20

8

1

Introduction

accomplished only in limited areas, and particular bodies in their complexities slip through this model. This is evident in Le Monde. Consistent with the epistemological project of the Regulae, Descartes’s first physical treatise provides a methodical study of nature. Despite his claim that he had inserted an account of the particular bodies on the earth,22 both the definition of nature as extended matter and the subsequent claim that bodies are compounds of matter with specific geometrical and kinematic properties, following specific laws of motions, and that one may know through equations, this system of physics suitably works for explaining nature in general, but not in particular. In Le Monde, there is no engagement with external varieties or particular bodies, as he mostly concentrates on a universal study of cosmological bodies. As a result, particular bodies remain a missing subject in his physics, jeopardizing Descartes’s philosophical program of constructing a universal science and extending his theoretical systematization to particular natures.

1.2

The Gaps in Descartes’s Study of Nature

The absence of a study of particular bodies had serious implications for Descartes’s investigation of nature as a whole. Besides a few smaller cases, Descartes’s mechanical framework fails to account for particular, individual bodies. In premodern times, the study of particular bodies gained momentum and developed through the collective efforts of natural histories, producing a serious attempt to catalog and possess the variety and singularity of nature,23 and define and describe particulars. Several scholars, from Conrad Gessner (1516–1565), Ulisses Aldrovandi (1522–1605), Carolus Clusius (1526–1609), among others, to seventeenth-century scholars such as Caspar Bahuin (1560–1624) and amateurs and collectors such as Nicolas-Claude Fabri de Peiresc (1580–1637), shaped premodern natural history, producing an outstanding (and sometimes unbounded) attempt to gather and order nature and its diverse bodies. Sometimes, the attraction to the diversity and overwhelming originality of rare, curious, or strange bodies slowly transformed into a fascination for the wonders of nature, typifying the Renaissance approach to natural diversity24 and somehow uncovering a heuristic role to teratologies and monstrosities in furthering scientific knowledge.25 As summarized by Ann Blair, this attention also surfaced in natural philosophers attracted by the variety of nature, as in Girolamo Cardano’s (1501–1576) De subtilitate (1550) and De rerum varietate (1557), or Jean Bodin’s

22

Discours de la Méthode, V, AT VI 43–44; CSM I 132–133. For a general overview, see Findlen 1994; Findlen 2006. Cf. Olmi 1992. Freedberg 2002. Ogilvie 2006. On Peiresc, see Reinbold 1990. Miller 2000. 24 On collecting, see Schnapper 1988. Findlen 1990. Pomian 1990. Bredekamp 1995. Daston and Park 1998. Cheng 2012. Patterson 2014. 25 See especially Brancher 2015; Brancher 2022. 23

1.2

The Gaps in Descartes’s Study of Nature

9

(1529–1596) Universae naturae theatrum (1596), and persisted through the early seventeenth century, for example in Francis Bacon’s (1561–1626) Sylva Sylvarum (1626). Notoriously, Descartes rejected history, that is, historical knowledge, as well as history of nature or natural history as a collection of particular bodies, as these sometimes entailed a fascination for strange bodies or the reduction of knowledge to catalogs of bodies and particular effects, that is, a descriptive account of the external characteristics of particulars, or the role of the sensory in acquiring knowledge.26 It is easy to claim that Descartes falls outside this list of scholars and this system of cumulating notions and experiences focusing on outward varieties.27 Accordingly, observing a large number of particulars is not necessary to attain deductive knowledge—a claim not far from Aristotle’s conception of scientia. First, Descartes reduces wonder and curiosity (which drove the collecting efforts of the time) to an epistemological error,28 and even to a form of mental disease.29 Second, he rejects history as a subjugation to authority and erudition and claims that knowledge is only an actual grasp of reason. Scientific knowledge belongs to the activities of the mind, intuiting and deducing the truth. Additionally, he rejects the cumulative efforts of observations and effects—and the information overload scholars pursued, such as Marin Mersenne, whom he believed to have too much curiosity, and who indeed collected effects in order to reach some knowledge.30 In contrast, Descartes aimed at the knowledge of the efficient cause.31 Third, his laboratory did not have the shape of a cabinet de curiosité, structured through the accumulation of naturalia, but appeared like a heated-stove room, empty of distractions (experiences or books) of any sort—but where dissections, observations of bodies, and chymical experimentation were performed and where epistolary exchanges thrived. Fourth, as we have seen, he conceived nature not as an assortment of diverse bodies but as a geometrical space measured by reason, an entity reduced to a mechanical set of processes on corpuscles. No space for particularities, rarities, or curiosities could surface. Within his rationalistic framework, all bodies are equal, and there is no need to observe a large number of particulars.

26

See Garrod 2018: 1–17. Cf. Lojacono 1990: 77–104. 28 Cf. Les Météores, AT VI 231, 366. 29 Cf. Regulae ad directionem ingenii, IV, AT X 371 and VIII, AT X 393; CSM I 15 and 28. La Recherche de la Vérité, AT X 499–500: “les corps des hydropiques n’est pas plus éloigné de son juste tempérament, que l’esprit de ceux-là qui sont perpétuellement travaillés d’une curiosité insatiable.” Les Passions de l’âme, II, art. 72–78, AT XI 382–386; CMS I 353–356. Cf. Peiresc, Lettre aux frères Dupuy, 27 September 1627, in Peiresc 1888–1889: vol. 1, 183: “ma maladie de curiosité est si mal satiable.” 30 One should note that Mersenne collected and discussed several curiosities in his text; cf. Marin Mersenne, “Question première: Quelles sont les principales curiositez qui occupend les hommes,” in Mersenne, Les Questions théologiques: 1–7. On information overload, see Blair 2010. MüllerWille and Charmantier 2012. On Mersenne, see Dear 1988. 31 Van Ruler 1995. Schmaltz 2014. 27

10

1

Introduction

Yet, along with the depiction of Descartes as a lone researcher, the description of Descartes as uninterested in nature and particular bodies, or as entirely committing to a gray ontology, is certainly far too extreme. While belonging neither to the side of scholars accumulating knowledge nor to those attracted by the wonders of nature, Descartes’s opposition to the study of natural particulars must be nuanced. Indeed, the knowledge of particular bodies and the study of nature significantly absorbed Descartes’s attention throughout his life in the Dutch Republic, as he attempted to apply his method to the entirety of nature. In the correspondence, he frequently discussed particular phenomena and curious bodies, exchanged bodies (such as seeds or specimens) and catalogs, or reflected on the role of experimentation, observation, lists of qualities, and natural history to experience what mechanical physics had established on a theoretical level. He also appealed to natural history and experimentation performed in line with Francis Bacon’s method, in order to corroborate a theory.32 Performed in accordance with his theory, these practical tools became an important addition to his rational epistemology, as they provided reason with data and information about nature in particular. The attention paid to particular phenomena indeed played a meaningful condition in Descartes’s study of physics, as he sometimes proved the validity of his theory via such particular, strange, or peculiar bodies. Moreover, toward the end of Principia philosophiae (1644), Descartes claims that “no phenomena of nature have been omitted,” as he explained from “size, figure, and motion {the varieties of} which I have explained as they are in each body,” and nothing “in the objects [is] other than, or at least perceived by us as nothing other than, certain dispositions of size, figure, and motion . . .” (Principia philosophiae, IV, art. 199, AT VIII-1 323; MM 282–283). Although his aspiration to produce an all-encompassing system of philosophy did not succeed entirely, the aim of this book is to unearth Descartes’s study of natural particulars, bridging the gap between his scientia and his investigation of particular bodies. Undoubtedly, Descartes’s work reveals an attention to nature in detail. Despite the fact that, as clearly stated by Stephen Gaukroger, “Descartes is usually approached through a single concern, namely the foundationalist metaphysics,” (Gaukroger 2002: 1) both the study of nature and a confrontation with particular bodies do not have a minor role in his philosophical project. The structure of Principia philosophiae evidently shows this concern, although he scaled back his initial ambitions. In summarizing its contents, in the letter he wrote as a preface to the French edition of the text, published in 1647, Descartes claimed that, after the metaphysics of Part 1, he devoted Part 2 to “physics, [. . .] discovering the true principles of material things,” then Part 3 to “the general composition of the entire universe,” and Part 4 to “the nature of this earth and all the bodies which are most commonly found upon it, such as air, water, fire, magnetic ore and other minerals” (Lettre-Préface to French edition of Principia philosophiae, AT IX 14; CSM I 186). Additionally, he had also planned “to examine individually the nature of plants, of

32

Milhaud 1921; Alexandrescu 2013. On Francis Bacon in France, Cassan 2014; Anstey 2018; Jalobeanu 2018a.

1.3 . . . and in Its Scholarship

11

animals and above all, of man” (Lettre-Préface to French edition of Principia philosophiae, AT IX 14; CSM I 186)33 in two parts he never accomplished. Despite the absence of the latter parts, the focus on the bodies of Part 4 is remarkable. If one counts the pages of each section, the difference between the topics is noticeable. Part 1 on the principles of human cognition counts 36 pages in the Adam-Tannery edition and Part 2 counts 39 pages, while Part 3 counts 120 pages, and Part 4 counts 125 pages, therefore testifying to the abundance of bodies he discussed in his study of nature.

1.3

. . . and in Its Scholarship

Still, historians and interpreters have generally dealt with Cartesian metaphysics, with his method, or with some specific segments of his physics, such as optics, cosmology, medicine, mechanics, or ethics, drawing less attention to Descartes’s natural philosophy in particular. As Roger Ariew has remarked, “Descartes produced at best only what could be called a general metaphysics and a partial physics” (Ariew 2014: ix).34 In this line, scholars have mostly concentrated on the foundational features of Descartes’s philosophy, sometimes analyzing how much the principles grounded a system of knowledge from a metaphysical and epistemological point of view. In Daniel Garber’s well-known book on Descartes’s physics, Descartes’ Metaphysical Physics, the author has importantly uncovered the link between metaphysics and physics but has not gone beyond this aspect. Later, Helen Hattab has explored several issues of Descartes’s mechanization of physics.35 The connection between the foundation of science and the sciences, that is, the link between the principles (Parts 1 & 2 of the Principia) and their application in the fields (Parts 4, 5, & 6) has remained largely unexplored or significantly under-explored. This book aims to fill this gap and investigate the application of Descartes’s method in the knowledge of particular natures, a complex feature of Descartes’s philosophical program. In a few important volumes and monographs, interpreters and historians have nonetheless engaged with a few aspects of Descartes’s natural philosophy. The essays collected in the volume edited by Jean-Robert Armogathe and Giulia Belgioioso, as well as in the volume edited by Stephen Gaukroger, John Schuster, and John Sutton, shed important light on the study of nature in Descartes’s

33 One should note that in article 188 of the fourth part of the Principia, Descartes stressed that his fifth part should have concerned “animals and plants,” apparently postponing the study of plants in favor of the study of animals, as it appears in Aristotle’s Meteorology; see Falcon 2015. 34 Ariew adds that “what Descartes produced was inadequate for the task [to rival to Scholastic textbooks].” 35 Garber 1992. Hattab 2009.

12

1

Introduction

philosophical project.36 The contributions to these volumes are a continuous reference for this book. A more significant work in this line is Stephen Gaukroger’s Descartes’ System of Natural Philosophy, in which the author examines the complete system of Cartesian philosophy, attempting to provide a comprehensive reconstruction of Descartes’s natural philosophy and filling its gaps. More recently, three works dealing with the study of bodies in Descartes have been published. In the first, Édouard Mehl discusses Descartes’s study of nature in the Principia. In the second, Bernard Joly explores Descartes’s engagement with chymistry and chymical bodies. And in the third, Vincent Aucante provides an outstanding attempt to systematize Descartes’s medical work within his philosophy.37 Besides these works, the focus on Descartes’s investigation of naturalistic bodies lags behind. The chapters of Part 1 of the recent Oxford Handbook on Descartes and Cartesianism, edited by Steven Nadler, Tad M. Schmaltz, and Delphine Antoine-Mahut, reveal the privileged areas of Cartesian studies, while little attention is given to the philosopher’s naturalistic investigations.38 Indeed, the contributions to the handbook concentrate on Descartes’s biography (including the intellectual background and the context), his method and epistemology, metaphysics (the mind, God, and freedom), mathematics, medicine, mechanics, the passions, moral philosophy, politics, and aesthetics, leaving therefore aside the application of his philosophy to the study of nature.

1.4

The Aim of This Book: Descartes’s History of Nature and Its Open Questions

The content of this book is positioned in the middle, between the study of Descartes’s metaphysics and metaphysical physics, his method, as well as his optics and cosmology, on the one hand, and his study of very particular sciences, such as medicine and ethics, or the human passions, on the other. In this book, I specifically deal with Descartes’s investigation of nature and natural bodies that populate the world—as Descartes himself claimed a central aspect of his physics: “From that I went on to speak of the earth in particular [. . .] how metals could appear in mines, plants grow in fields, and generally how all the bodies we call ‘mixed’ or ‘composite’ could come into being there” (Discours de la Méthode, V, AT VI 43–44; CSM I 133). Following Descartes’s representation of his philosophy as a tree, this book concentrates on the trunk (i.e., his physics as an interpretation of nature) and the

36

Cf. Armogathe and Belgioioso 1996. Gaukroger et al. 2000. Cf. Mehl 2009. Joly 2011. Aucante 2006a. On Descartes’s meteorology, I should mention Martin 2011: 125–147. I have more recently published a book on Descartes’s medicine, see Baldassarri 2021a. 38 Nadler et al. 2019. See my review of the volume, which I consider a precious piece of scholarship; cf. Baldassarri 2020a. 37

1.4

The Aim of This Book: Descartes’s History of Nature and Its Open Questions

13

early branches before the three main disciplines, medicine, mechanics, and ethics. This book deals with those disciplines that deal with minerals, metals, and rocks in general (mineralogy or chymistry), plants (botany), and animals (zoology), certainly, the spheres in which the application of his mechanical reduction appears more difficult.39 It is to be noted that these disciplines have no autonomous status in Descartes’s system of natural philosophy, as he reduces them to his physics, that is, to matter and motion—for instance, his mineralogy heavily relies on his meteorology. This mechanization is consistent with his refusal of both the Aristotelian uses of substantial forms and souls to arrange nature in a scale of bodies and the natural historical attempt to gather all varieties in order to understand nature. All nature should be reduced to the unity of extended matter, as well as all disciplines should be reduced to physics. In this sense, no scale of bodies surfaces in Descartes’s mechanical nature, except for a difference in quantification that uncovers a mechanical complexity.40 This, however, reveals a difficult point. In the Discours, for instance, Descartes claims that a difference surfaces between the “very few parts [of a clock], in comparison with the great multitude of bones, muscles, nerves, arteries, veins and all the other parts that are in the body of any animal” (Discours de la Méthode, V, AT VI 56; CSM I 139). A mechanical gradation or hierarchy ultimately emerges. This also arises earlier in the text, where Descartes points out a divide between the study of “inanimate bodies and plants” and the description of “animals, and in particular men” (Discours de la Méthode, V, AT VI 45; CSM I 134). In claiming that he has not “sufficient knowledge to speak of [animals and men] in the same manner [of previous bodies],” he intends that he had followed a chain of reasoning from the causes to the effects to explain minerals and plants, while he could not follow the same line for the other bodies. The question is whether his reduction of nature to extended matter works for inanimate bodies as well as for living bodies, or if differences arise—and, if yes, where exactly. This not only appears to be an epistemological difference but also seems to entail a hierarchical gradation between bodies, which is not inconsistent with Descartes’s metaphysics.41 While I leave aside the connections between metaphysics and physics, in this book, I focus on the question of bodily hierarchy in Descartes’s physics. An inconsistency, however, arises. On the one hand, having claimed that nature is a piece of matter without qualitative differences but a quantitative complexity (which is methodologically reducible to the unity of reason) entails that all bodies are

In a very recent article, Theo Verbeek has claimed that there is “a centrifugal force” in Descartes’s philosophy, “which made it possible to separate medicine and moral philosophy from physics, and physics from metaphysics” (Verbeek 2023: 33). 40 Especially during the Renaissance, the ancient idea of a scale-of-beings as a hierarchy moving from the most to the least perfect beings had been revived, but Descartes’s ontology opposes this graduation. See Lovejoy 1936. 41 Cf. Agostini 2022. 39

14

1

Introduction

equal.42 On the other hand, a mechanical gradation apparently develops, for instance, in the differentiation between nonliving and living bodies, while understanding this point remains difficult. This differentiation seems to follow the grades of mechanical complexity, according to which some bodies are more complex than others from a mere mechanical point of view. While this is consistent with his interpretation of nature as a source of activities and changes, in which particular bodies take shapes and differentiate, forming all composites and mixtures, a problem surfaces in defining bodies’ individuality within his mechanical physics. This is easier in the case of minerals and stones, as an identification between a metal in general and a metal in particular develops, but the same cannot be easily said of plants and animals, despite Descartes’s claim of the Lettre-Preface examined earlier.43 In the case of living bodies, the mechanical reduction applies for a general interpretation but fails to specify for individual, particular bodies, and living bodies’ individuality is much more difficult to define within his mechanical framework.44 In focusing on particular, existing bodies, I explore Descartes’s application of his mechanical reduction to living bodies, evaluating whether or not it works in the same ways for minerals, stones, rocks, plants, and animals, and where the difference lies. In the text of the Discours just quoted, the nature of plants stands in the middle between minerals and animals. Plants were a problematic subject in early modern natural philosophy altogether, and they have a quite ambiguous and fluctuating status in Descartes. In 1637, he bracketed plants together with inert bodies, whereas in the Principia, he plans a section on plants together with animals as living bodies. For this reason, Descartes’s mechanization of plants reveals as a major issue in his program, for vegetal bodies—which Descartes equals to vegetation—apparently share something with minerals and stones, as well as with animals. Defining them closer to either minerals or animals entails significant consequences in his philosophy. A clear divide seems to emerge in his understanding of natural bodies. Indeed, while the reduction of chymistry to his mechanics is more or less effective, despite rejecting the autonomy of chymistry, the reduction of animals to the mechanical patterns of his physics is more and more problematic. Descartes consistently conceived animals as automata but at the same time tended to recognize an ontic or systemic organization of animal bodies that proceeds beyond the mechanical reduction. The text of the Discours seems to acknowledge such a differentiation between bodies, as the more complex nature of some of them makes any mechanization insufficient. This is why Descartes could not describe animals and men in the same ways as inert bodies (and plants), as he claims in the text. A sort of mechanical

42

I do not enter into Descartes’s comparison between natural and artificial bodies; see, for instance, Principia philosophiae, IV, art. 203, AT VIII-1 326. 43 Lettre-Préface, AT IX 14; CSM I 186. 44 See the classic, Rodis-Lewis 1950. Grosholz 1994; de Buzon 1995; Alexandrescu 2009; Reid 2014; Toth 2022. Some of these issues are treated in Chap. 3 of this book.

1.5

The Matter of This Book

15

differentiation therefore emerges in Descartes’s philosophy of nature. Accordingly, minerals, stones, and rocks stand on a lower grade of the scale, while animals and men have a more complex body, and their explanation should consider their mechanical complexity. Plants stand in between them. Where the difference lies remains, however, unclear. It is possible that this resides in sensation (and selfmovement), as animals and human bodies show a sensorial answer, while plants, stones, and rocks do not. Whether this entails a differentiation between nonliving and living bodies is, however, problematic. Later in his work, Descartes bracketed plants among living bodies, although they have no sensation (besides the case of the sensitive herb, which is a matter of discussion in Chap. 5). In this book, I discuss the details of this possible mechanical gradation within particular bodies, and the problematic condition of plants, while I do not deal with the difference between men and animals, a topic that has attracted enormous attention in Cartesian studies, falling under medicine and physiology. Finally, I deal with a last issue. While it is possible to establish a study of minerals and rocks in his program, as he devoted the fourth part of the Principia to these bodies, the problems arising in the other fields made it impossible for Descartes to publish any treatise (or sections) on plants and animals. Filling the gaps in Descartes’s study of nature uncovers a set of diverse obstacles. Although Gaukroger and Mehl have already attempted to bring Descartes’s system of nature to completion, this book aims to shed a diverse light on these topics. Both scholars have mostly dealt with reconstructing the sections of Principia philosophiae, moving from Descartes’s metaphysics, and, following the text, they have proved able to present the contents of his school text, ultimately shaping Descartes’s entire system of philosophy. In this book, I follow a different path. In concentrating on Descartes’s correspondence, posthumous works (such as the Latin biomedical manuscripts), and published materials, my aim is to investigate Descartes’s experimental observation of natural particulars, discussing the matters he could include in the sections on rocks, stones, minerals, plants, and animals composing his natural philosophy, and how much these develop from, and are consistent with his metaphysics. Moving from his method, which reduces knowledge of all nature to the mathesis universalis, i.e., a universal science grounded in reason, and from his mechanical physics, which consists of reducing nature to extended matter in motion, the goal of this book is thus to deal with Descartes’s account of particular natures or mixtures, ultimately clarifying whether a universal science of natural bodies develops from a small set of explanatory principles.

1.5

The Matter of This Book

This book is divided into two main parts. In the first, I explore Descartes’s method and his definition and construction of nature, that is, the application of his method to the knowledge of nature. The two chapters composing this part are related, as the changes that Descartes’s method underwent throughout the years parallel the

16

1

Introduction

changes in his interpretations of nature. In the second part, I investigate his studies of the particular bodies that populate the world, revealing the differences as he moved from inert bodies to living beings. In Chap. 2, I discuss Descartes’s method in relation to the knowledge of particular bodies. First, I examine his rejection of history and the definition of scientia as an actual grasp of reason. The latter shapes the method of the Regulae, whose procedures (namely the disposition in series, comparison, enumeration, and induction) help acquire certain knowledge in all disciplines. While knowledge replicates the order of mathematics, Descartes claims that science is a combination of deduction and experimentation. He fleshes out this combination in his early 1630s correspondences with Beeckman and Mersenne, where he outlines experimentation, lists of qualities, natural history, and observations as crucial tools to acquire knowledge of particular bodies. Later in the Discours, Essays, and Principia, Descartes opens out to hypotheses, suppositions, and a posteriori knowledge, showing significant changes in his method as he aims to construct a more exhaustive philosophy of nature. In Chap. 3, I present Descartes’s definition of nature as extended matter, displaying the three ways of systematizing nature pursued by Descartes. First, I discuss his invention of nature by means of imagination, as it occurs in Le Monde. Second, I present his attempt to construct nature by means of the mechanical rules of motions, by means of which particular bodies arise from the continuity of extended matter. Third, I focus on Descartes’s description of particular bodies, especially uncovering the role of observation in the study of physics. From Le Monde to Les Météores and the Principia, I unearth the changes in Descartes’s ways of defining and systematizing nature. While in Le Monde he conceives nature by means of a mathematical equation, therefore making it a construction of the mind (paralleling the epistemology of the Regulae), in Les Mététores and in the Principia, particular phenomena are at the center of his enterprise. As Descartes moves from the whole of nature to describing particular bodies, experimentation plays a more substantial role in verifying his philosophy, and the observation of natural particulars acquires a scientific stature. From Chap. 4 to Chap. 6, I deal with Descartes’s study of particular bodies in more detail. Following the division of the Principia, I focus first on stones, rocks, minerals, and metals in Chap. 4, then on plants and vegetal bodies in Chap. 5, and finally on animals and brutes in Chap. 6. The aim of these chapters is to explore Descartes’s investigations of these diverse natures, as he attempted to provide an explanation of their nature, functioning, and characteristics, and how much these fit (and develop from) his mechanical physics. Yet, there are major differences between his attempts to deal with minerals and stones, plants, and animals. A mechanical explanation of the functioning of inert bodies appears more consistent with his mechanical physics, while a mechanization of living nature presents flaws and limitations. As I show in the chapters, Descartes’s path toward the mechanization of nature was not linear or without problems. In Chap. 4, his reduction of chymistry to physics (consistent with his rejection of alchemy) thwarts his explanation of the differentiation between minerals, metals,

1.5

The Matter of This Book

17

fossils, and rocks. In Chap. 5, the reduction of plants to hydraulic machines faces serious limitations, as the mechanization of the basic (or vegetative) activities of life encounters difficulties in defining the life of his philosophical program. Growing difficulties characterize the study of animals. In Chap. 6, I investigate Descartes’s attempt to balance the animal-machine model and the explanation of instincts, spirits, and animal life, which apparently overcome an interpretation of animals as utterly mechanical. This tension between the mechanical reduction, which serves to explain the living functions per se, and the investigation of the animal body as a whole, or as a system, persists throughout Descartes’s texts, as in his Latin biomedical manuscripts a sort of hierarchy among animals surfaces. Finally, problems arise in differentiating between animals, brutes, and humans, while Descartes ultimately conceived life as an organic, coherent unity of processes and functions. In the chapters, I tackle all these problems, limitations, and challenges that concern Descartes’s attempt to explain particular bodies consistently with his philosophical program of mechanizing nature, that is, by means of mathematical demonstration. Instead of a system a priori, in dealing with particular bodies, Descartes’s science develops from a posteriori reasoning, that is, from observations and experimentation (and hypotheses) through which he moved back to the causes. In collecting Descartes’s entire attention to particular bodies from his published and posthumous work and correspondence, I also deal with curious cases such as the Bologna Stone and the sensitive herb, laying bare a Cartesian attempt to reconstruct a universal science and produce a history of natural phenomena methodologically framed and mechanically explained. Such an original natural history results from the combination of his rationalistic project, his ontological definition of nature as extended matter composed of particles in motion, and the reduction of particular bodies to his theoretical framework.45 Investigating the application of his method to the study of nature, in this book I show to what extent Descartes successfully reduced the diverse sciences, namely chymistry, botany, and zoology, to his mechanical physics and to the principles of his philosophy, ultimately combining the study of particular, individual bodies with the aim to construct a universal science grounded in the clear and distinct ideas of the mind and bridging the gaps between his metaphysics and the investigation of particular bodies.

45

I therefore disagree with the recent book by Deborah Brown and Calvin Normore claiming that Descartes’s investigation of natural bodies is a sort of ontology of everyday life; cf. Brown and Normore 2020. See my book review: Baldassarri 2021b. See also Cunning 2023.

Chapter 2

Method

Abstract In defining a method to know nature, Descartes forms it on the certainty of mathematics and on the operations of the intellect. His epistemology, especially as developed in Regulae ad directionem ingenii, appears quite rationalistic. Yet, as he applied it in the actual investigation of nature, he claimed that one achieves knowledge through a combination of deduction and experimentation, as experience and hypotheses acquired importance through time. In this chapter, I explore Descartes’s attempts to adjust his epistemology to attain a sound knowledge of nature (from Regulae ad directionem ingenii and the correspondence with Beeckman and Mersenne to the Discours and the correspondence with Morin, and finally to the method of Principia philosophiae). As Descartes became involved in actual empirical research to achieve complete physics, his epistemology changed. In Rule 4 of Regulae ad directionem ingenii, Descartes writes that “it is far better never to contemplate investigating the truth about any matter than to do so without a method” (Regulae ad directionem ingenii IV, AT X 371; CSM I 16).1 Accordingly, a method is necessary to discover knowledge and find the truth in any discipline, as the truth one might know by chance is generally useless.2 In 1637, Descartes introduced his essays on natural philosophy, namely La Dioptrique, Les Météores, and La Geometrie, along with a short discourse in which he disclosed the importance of a method to achieve this goal. In the history of philosophy, the Discours de la Méthode is a masterpiece, and “few subjects have received more scholarly attention in the history of philosophy than Descartes’s method” (Weber 1972).3 Here, I will not deal with all the features of the method or the Discours. Specifically, I will not deal with the subjects that have received the most attention from historians and philosophers, 1

A rich investigation of the Regulae ad directionem ingenii is in Beck 1952. Grosholz 1991. Sepper 1996. 2 Descartes provides several examples about such a case. One is in the famous letter to Beeckman, October 17, 1630, AT X 161. Another is in La Description du corps humain, II, AT XI 245. 3 Translation is mine; original French is: “Peu de sujets ont été autant étudiés, dans l’histoire de la philosophie, que la Méthode cartésienne.” Cf. Dika 2020. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 F. Baldassarri, René Descartes’s Natural Philosophy and Particular Bodies, Studies in History and Philosophy of Science 60, https://doi.org/10.1007/978-3-031-48663-0_2

19

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Method

that is, the relationship between logic, method, and mathematics. I will also elide the study of how Descartes’s method fits into the larger early modern context, certainly an important section of any work on Descartes’s philosophy.4 Instead, I will deal with Descartes’s application of his method in order to know nature and particular bodies, the subject of this book. I am much more interested in seeing how Descartes combined a method that mostly consists of an ars cogitandi with the knowledge of particular bodies or phenomena, in order to attain a universal science.5 While Scholastic philosophy claimed that knowledge of principles comes from experience, and demonstration from effects to causes, and while scholars of the time tried to fill the gap between the order of knowledge and the system of nature by means of collections and natural history, Descartes deemed these kinds of knowledge to be accidental and provisory. He presented an alternative method to Aristotelian syllogism and to the early modern collections of natural varieties that generally fell under the natural historical quest for a systematic understanding of particular bodies.6 Still, I am aware of the problems this investigation entails. First of all, in the 1638 letter to Jesuit professor of logic, physics, and mathematics, Antoine Vatier (1591–1659), when asked about the method in the three essays, Descartes wrote that: “I could not demonstrate the use of this method in the three treatises which I gave, because it prescribes an order of research which is quite different from the one I thought proper for exposition” (Descartes to Vatier, February 22, 1638, AT I 559; CSMK 85).7 In this sense, applying the method to natural things appears quite difficult. An exception to this is the case of a rainbow on which historians and interpreters have devoted crucial attention. A second issue is that, as Tarek Dika has recently pointed out, the interconnection of sciences in the Regulae, where he defines the method as mathesis universalis, cannot constitute a system—for this reason, Descartes “abandons mathesis universalis and redefines the object of mathematics” (Dika 2023: 319).8 Moreover, despite the claims of the Regulae that proposes a very rationalistic epistemology—for instance, he favored a method grounded on the activities of the mind, for there is “no knowledge without mental intuition or deduction” (Regulae ad directionem ingenii, IV, AT X 372; CSM I 16) and science is an act of intellectual cognition—a more complex picture surfaces in the path for knowledge. This is especially true when he aims to apply his epistemology to the knowledge of particular bodies.

4

On methodology in the early modern context, see Reiss 2001. Efal-Lautenschläger 2022. Sgarbi 2023. 5 I would argue that Descartes’s method and logic have a similar condition. See Ariew 2021. 6 On these cases, see Jardine and Spary 2018; Pomata 2005. 7 See Conversation with Burman, AT V 153; CSMK 338. 8 However, the problem remains complex, especially in the light of the absence of mathesis universalis in the manuscript of the Regulae recently discovered in Cambridge. See Serjeantson and Edwards 2023.

2

Method

21

Nevertheless, my interpretation is that both Descartes’s description of several methodical procedures in the Regulae, which restore the importance of experimentation and observation, and the attention to natural history and the collection of natural particulars gained momentum as he developed a treatise on physics. Experiments, observations, lists of qualities, and collections appear as crucial aids to intellectual knowledge, as they provide theory and principles with data, making the former operative. Still, the mind must operate on experimentation, making the latter intelligible. In fact, from the rationalistic epistemology of the Regulae, when abandoning the method of this early text, Descartes opened to experimentation and to a posteriori knowledge, that is, from the effects to the cause, revealing the significant changes his epistemology underwent over the years. In the Discours, for instance, hypotheses and suppositions help Cartesian knowledge when the chain of deduction is interrupted, as importantly discussed by Daniel Garber.9 A turning point apparently developed as Descartes debated his epistemology with his correspondents, who forced him to explore (and explain) particular natures. This is particularly evident if we compare Rule 3 of Regulae ad directionem ingenii with Parts 3 and 4 of Principia philosophiae. In the first text, Descartes claimed that scientific knowledge [scientia] and history are not just two different segments of knowledge, but appear unrelated.10 Accordingly, Science consists of the intellectual ability to solve problems or to demonstrate and explain a subject, while history appears just as an erudite collection of notions, if not even a discipline that alters or exaggerates matters, and for this reason, it cannot be entirely trusted.11 In Parts 3 and 4 of Principia philosophiae, where he proposed to achieve “a brief history [historiam] of the principal natural phenomena” (Principia philosophiae III, art. 4, AT VIII-1 81 [translation is mine]) as a way to make the mind able to deal with the innumerable particular bodies of nature and produce a more exhaustive physics. In this chapter, I explore the changes (and perhaps the evolution) of Descartes’s epistemology from the extreme rationalism of the Regulae to the increasing importance of experience and hypothetical reasoning in his later epistemological practice, which more and more departs from the rigid method of his early text. However, as I try to demonstrate, already in the Regulae there is an opening to this transformation, especially as he appealed to a few methodological procedures. In the first section of this chapter, I present Descartes’s rejection of history and of any attempt to infer knowledge from the accumulation of objects and opinions, while he defined scientific knowledge as an actual grasp of reason alone. In the second section, I show how experimentation was part of Descartes’s epistemology, whose Cf. Garber, “Descartes and Experiment in the Discourse and Essays,” in Garber 2001, p. 109. Regulae ad directionem ingenii III, AT X 367; CSM I 13: “and even though we have read all the arguments of Plato and Aristotle, we shall never become philosophers if we are unable to make a sound judgement [. . .]; in this case what we would seem to have learnt would not be science but history.” Differently from Descartes, Francis Bacon had proposed to embed natural history with a modern logic. On the relation between Descartes and Bacon, see Cassan 2014. Cf. Jalobeanu 2015. 11 Discours de la Méthode I, AT VI 7; CSM I 114. 9

10

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Method

seed was already present in the Regulae and how often he asked for histories and descriptions of phenomena from his correspondents in order to fill in the gaps in his system. Still, the appeal to experimentation shaped Descartes’s epistemology through the years, while importance changes surface. In the third section, I show Descartes’s experimentation in the system of his natural philosophy, focusing on the Discours, Essays, and Principia—in these texts, experimentation, suppositions, histories, and hypotheses played a relevant role while he attained a more exhaustive explanation of particular bodies.

2.1 2.1.1

The End of History and a New Scientia Against History

In a juvenile fragment, collected in Studium bonae mentis, Descartes wrote against the Ancients and their alleged superiority in the sciences. This is the text: We should not attribute much to Ancient [scholars] because of their antiquity [antiquitatem]. In contrast, we should be said more ancient than they should. Today, the world is older [senior est] than when they lived, and we have more experience of things [than they did]. (Studium bonae mentis, AT X 204 [translation is mine])12

Within the traditional claim of moderns [novatores] as dwarves on the shoulders of giants—a medieval allegory revived in the Renaissance—Descartes proposed an original interpretation. Accordingly, it is no more a matter of authority or antiquity, but of experience. In this sense, history does not teach the truth, and knowledge belongs neither to the past nor to the authority of ancient scholars, but rather to the present, for the actual experience of things grounds one’s knowledge. This is what he writes to Isaac Beeckman in the famous October 1630 letter. According to Descartes, anyone who truly knows something is able to demonstrate his knowledge each time, without referring to anything written in a journal.13 Knowledge is an actual activity and not a recollection of authorial claims or opinions. Knowing something from the past or knowing something by heart (i.e., the recollection from memory) is not true knowledge for Descartes. Throughout his works, Descartes repeated similar claims against memory, books, and bookish knowledge. In Regulae ad directionem ingenii, for instance, he claims that while “we ought to read the writings of the ancients [. . .] in order to learn what truths have already been discovered [. . .],” one must avoid the dangers of being too close to them, as “traces of their errors will infect us and cling to us against our will”

Original Latin is: “Non est quo Antiquius multum tribuamus propter Antiquitatem; sed, nos potius iis antiquiores dicendi. Jam enim senior est mundus quam tunc, majoremque habemus rerum experientiam.” 13 Descartes to Beeckman, October 17, 1630, AT I 160–161. On Descartes and Beeckman, see de Buzon 2013; Van Berkel 2013. On Isaac Beeckman, see van Berkel et al. 2022. 12

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The End of History and a New Scientia

23

(Regulae ad directionem ingenii III, AT X 366; CSM I 13). It is not that books are dangerous per se, but rather that by relying too much on them, one fails to understand whether they contain anything incorrect. Relying on books results in uncertainty. Knowledge is not merely acquiring an argument or gathering a number of opinions, that is, what one achieves through reading. Rather, in contrast to this, Descartes claimed that knowledge is an exercise of the ingenium or mind. He writes: even though we know other people’s demonstrations by heart, we shall never become mathematicians if we lack the intellectual aptitude to solve any given problem. And even though we have read all the arguments of Plato and Aristotle, we shall never become philosophers if we are unable to make a sound judgement on matters which come up for discussion; in this case what we would seem to have learnt would not be science but history. (Regulae ad directionem ingenii III, AT X 367; CSM I 13)

Accordingly, knowing someone’s opinion consists of knowing the doctrine of an author, that is, possessing historical knowledge. Although this latter may be correct, “we would always be uncertain which of them [. . .] to believe” (Regulae ad directionem ingenii III, AT X 367; CSM I 13). In learning Plato’s or Aristotle’s texts, one would know their argument, according to Descartes, but not whether these arguments are true. In this sense, one would know the history of philosophy, but would not be a philosopher. Descartes thus distinguishes between the knowledge of truth, what he calls scientia, or the ability to produce knowledge or solve problems, and the knowledge of someone else’s doctrines, what he calls historia, that is, a corpus of propositions. In 1640 to Corneliis van Hogelande (ca.1590–1662), Descartes repeated a similar claim: “in mathematics, I distinguish between history and science. By History [Historiam], I understand everything which has been discovered already, and is contained in books. By Science [Scientiam], I mean the ability to solve every problem, and thus to discover by one’s own efforts [. . .] anything that could be discovered by means of our native human intelligence” (Descartes to Hogelande, February 8, 1640, AT III 722; CSMK 144 [translation slightly modified]). The difference is noticeable.14 Along with this line, in the Discours de la Méthode, he affirms that reading the books of ancient scholars, namely “their history and fables” (Discours de la Méthode I, AT VI 7; CSM I 113) does not help one make a sound judgment about an argument, but only to know their opinion. Descartes differentiated between (1A) having learned an argument (including a mathematical demonstration that one may know by heart), or (1B) having gathered diverse doctrines or facts, and (2) being able to judge and evaluate something (or solve a problem and differentiate between true and false). Scientific knowledge belongs to the latter case and pertains to intellectual activity—for his predecessors, in contrast, having science means having a set of knowledge, formally encapsulated within a tradition. In Rule 10, Descartes expresses this point through a biographical example. He writes:

14

Dika 2023: 60.

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Method

The natural bent of my mind, I confess, is such that the greatest pleasure I have taken in my studies has always come not from accepting the arguments of others but from discovering arguments by my own efforts. [. . .] Whenever the title of a book gave promise of a new discovery, before I read any further I would try and see whether perhaps I could achieve a similar result by means of a certain innate discernment. (Regulae ad directionem ingenii X, AT X 403; CSM I 35)

In contrast to collecting notions from books, knowledge consists in discovering something by means of innate discernment. Knowledge thus belongs to the mind, as one knows through the operations of reason. Descartes referred to it as the strength of the ingenium, the order of the mind, or the power of the intellect. In any case, he specified knowledge as an activity of reason, to which our ingenium suffices,15 and differentiated it from any mere opinion acquired from books or through the authority of someone else. This differentiation also surfaces in Descartes’s opposition to Scholastic tradition and schooling, as he claimed that education, intended as the acquisition of someone else’s opinions, is inefficacious to acquire true knowledge. In the Discours, he suggested that Scholastic formal logic and the syllogism are connected to the accumulation of opinions from books, generally performed by the hommes de lettres.16 Accordingly, “syllogisms [. . .] are of less use for learning things than for explaining to others the things one already knows or even [. . .] for speaking without judgement about matters of which one is ignorant” (Discours de la Méthode II, AT VI 17; CSM I 119).17 For Descartes, the false logic of syllogism results in incorrect knowledge, namely in speaking without judgement or cognition. In the Regulae, he states that “dialecticians are unable to formulate a syllogism with a true conclusion, [. . .] unless they have previous knowledge of the very truth deduced in the syllogism. It is obvious therefore that they can learn nothing new from such forms of reasoning. Its sole advantage is that it sometimes enables us to explain to others arguments which are already known.”18 Besides the speculations and errors such as petitio principii, it appears that syllogism is mostly useful to win disputes and controversies and generally operates by gathering and ordering opinions and notions.19 15 Regulae ad directionem ingenii, II, AT X 362: “Circa illa tantum objecta oportet versari, ad quorum certam et indubitatam cognitionem nostra ingenia videntur sufficere.” One should also note that, according to Descartes, it is unfair to claim that truth cannot be in books, the point is that anyone should be able to discover truth, not just reading and repeating it. Regulae ad directionem ingenii II, AT X 362; CSM I 10. Cf. Robinet 2000. Baldassarri 2016. 16 Discours de la Méthode, I, AT VI 10; CSM I 115. Cf. Petrescu 2018. 17 On Descartes and syllogism, see Gaukroger 1989: pp. 6–25. 18 Regulae ad directionem ingenii, X, AT X 406; CSM I 36–37. 19 Discours de la Méthode VI, AT VI 69; CSM I 146: “Nor have I ever observed that any previously unknown truth has been discovered by means of the disputations practised in the schools. For so long as each side strives for victory, more effort is put into establishing plausibility than in weighing reasons [. . .]; and those who have long been good advocates do not necessarily go on to make better judges.” Cf. Regulae ad directionem ingenii, II, AT X 363; CSM I 11: “syllogisms [. . .] are just made for controversies. For these exercise the minds of the young, stimulating them with a certain

2.1

The End of History and a New Scientia

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In opposition to Scholastic logic, Descartes developed an alternative epistemology, expounded in Regulae ad directionem ingenii. This treatise was probably written by Descartes in the late 1620s and early 1630s, left incomplete and later re-elaborated with several additions, possibly during the late 1630s.20 It, however, remained incomplete and was published posthumously. Still, it contains an extended investigation of the nature of Descartes’s logic and method, which at this stage is called mathesis universalis.21 In particular, the Regulae unearths a cognitive productivity of the mind, which Descartes used to counteract traditional systems. Moving from his opposition to history and any system grounded on the accumulation of notions, in the next section, I investigate his definition of knowledge as an actual grasp of reason.

2.1.2

Descartes’s Scientia and His Method

In rejecting Scholastic knowledge based on books, Descartes claimed that reason alone is able to acquire scientific knowledge, namely to discover truth. The reason lies at the center of any investigation. In this sense, Descartes rejected the scholastic priority of objects as bearing any truth (which one may know through sensation) and claimed that “all the sciences are nothing other than human wisdom [humana sapientia], which always remains one and the same, however, applied to different subjects” (Regulae ad directionem ingenii, I, AT X 360; H 65).22 Accordingly, scientific knowledge is an act of reason, for “the intellect alone is capable of scientia,” and reason does not change when applied to diverse disciplines, but produces a universal sapientia (wisdom). Yet, cultivating the mind not only consists of increasing the natural light of reason, through which one acquires knowledge, but also consists of applying the power of reason to all diverse objects. Everything may be the object of knowledge insofar as it is “susceptible of investigation by the human mind” (Regulae ad directionem ingenii, VIII, AT X 398; H 121).23 These subjects include “the virtues of plants, the motions of stars, the transmutations of metals, and the objects of similar disciplines” (Regulae ad directionem ingenii, I, AT X 360; H 65). This is a crucial passage, for it reveals that in principle cognition operates on all disciplines and particular bodies.

rivalry . . .” See also: Lettre-Préface, AT IX-2 13–14; CMS I 186: in contrast to “the logic of the Schools [which is] nothing but a dialectic [that] teaches ways of expounding to others what one already knows or even of holding forth without judgement about things one does not know,” one should prefer the “logic which teaches us to direct our reason with a view to discovering the truths of which we are ignorant.” 20 Serjeantson and Edwards 2023. 21 See Garrod and Marr 2021. Cf. Dika 2023: 120–140. 22 See Dika 2023: 53–57. 23 See Smith 2010: pp. 113–123.

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Method

However, applying the human mind to all subjects remains a matter of investigation. As he writes in Rule 2, “all knowledge [omnis scientia] is certain and evident cognition” (Regulae ad directionem ingenii, II, AT 362; CSM I 10) and therefore consists of making any object of knowledge conform to the intellect. Knowledge is an ars cogitandi of the subject, and to know something consists in reducing everything to reason. How does this reduction work? The solution is rather complex. In Rule 2, Descartes suggests reducing the object of knowledge to a mathematical computation. Mathematics offers Descartes with an example of certainty, insofar as “they are concerned with an object so pure and simple that they make no assumptions that experience might render uncertain; they consist entirely in deducing conclusions by means of rational arguments” (Regulae ad directionem ingenii, II, AT 365; CSM I 12). Since their object is abstract, it resides in the mind, and no experience could ever blur its knowledge. Moreover, moving from premise to conclusions is a matter of rational deductions, as no experimentation is required. In being purely rational, mathematics appears as “the easiest and clearest of all the sciences” (Regulae ad directionem ingenii, II, AT 365; CSM I 12) and develops as a suitable example to comprehend the ways one achieves scientific knowledge. Yet, Descartes conceives of mathematics as a model and in Rule 3 proceeds further beyond them. Here, he moves from a singular discipline, namely mathematics, to mental cognition, as he claims that knowledge can only be attained by the activities of reason, i.e., intuition and deduction.24 The first consists in understanding a single proposition (or a simple nature), a point of departure that provides undoubtable knowledge of something.25 This simple nature is an idea that does not need any other ideas to be known and is conceived immediately and directly. For example, “a triangle is bounded by just three lines” or “a sphere [is bounded] by a single surface” (Regulae ad directionem ingenii, III, AT X 368; CSM I 14) and so on. The second is the ability to infer something from these basic propositions or first principles. While intuition is a singular point of reasoning by which one can instantaneously grasp first principles, deduction is a chain of reasons that moves from principles to effects. In operating on the object of investigation, these intellectual operations construct scientific knowledge by reducing the object to ideas (i.e., analysis) and by deducing all knowledge from these ideas (i.e., synthesis). Yet, when one moves from the epistemological ground (and from mathematics) to more complex disciplines, such as the study of the virtues of plants, transmutations of metals, and so on, a method appears mandatory to Descartes, as knowledge is more difficult of attainment. In Rule 4, Descartes writes that the method works in extending the certainty of the intellect and applying its operations (and the certainty of mathematics) on diverse disciplines. In this sense, the method has no suitable

Regulae ad directionem ingenii, III, AT 366; CSM I 13: “Concerning objects proposed for study, we ought to investigate what we can clearly and evidently intuit or deduce with certainty [. . .]. For knowledge can be attained in no other way.” On intuition, see Paul 2023. 25 Cf. Garber and Cohen 1984. de Buzon 2021; Guidi 2021a. On simple natures, see Marion 1992. 24

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object, as it works in the same way as it involves “numbers, shapes, stars, sounds, or any other object whatever” (Regulae ad directionem ingenii, III, AT X 378; CSM I 19). This is what he calls mathesis universalis and works for not only in mathematics (which is the privileged discipline of knowledge) but also in fields such as cosmology, musicology, or any other discipline, insofar as the knowledge in these fields concerns the problems of order and measure. The universality of the method is also confirmed by the fact that it is formed on the intellect, which is universal, and not singular objects. Instead, one should make the singular object conform to intellectual activity.26 In Rule 5, Descartes consistently claims that “the method consists entirely in the ordering and arranging of the objects on which we must concentrate our mind’s eye [mentis acies] if we are to discover some truth” (Regulae ad directionem ingenii, V, AT X 379; CSM I 20). Knowledge thus consists of defining a rational order and measure of things, and the method works producing the connection between the mind and particular objects. In the following rules, Descartes specifies the procedures of the method to achieve knowledge in every discipline. In Rules 6 and 7, he describes the operations of his method to perform reduction and reconstruction27; these are relation, series, comparison, enumeration, and induction, which help complete scientia [ad scientiae complementum] and provide the knowledge of any objects within a mental order. In Rule 6, he investigates series and comparisons, which arrange objects through mental consideration, and not by referring to an ontological genus, as was the case with the scholastic system.28 In Rule 7, he describes enumeration and induction, which unify classes of disconnected and diverse objects to a singular point [unum quid] through mental arbitrio, that is, by reducing the variety of objects to ideas.29 These operations order the objects of knowledge through reason, ultimately aiming at reducing nature to intelligible patterns.30 I investigate these procedures in the following pages. The balance between the method and the intellect is the leitmotif of Rule 8, where Descartes stresses the importance of defining the extension and limitations of human knowledge. At this point, Descartes makes an important comparison between the method and the mechanical crafts, “which have no need of methods other than their own, and which supply their own instructions for making their own tools” (Regulae ad directionem ingenii, VIII, AT 397; CSM I 31). He thus makes the example of the blacksmith. If someone wanted to practice one of these crafts—to become a blacksmith [. . .]—but did not possess any of the tools, he would be forced at first to use a hard stone [. . .] as an anvil, to make a rock do as a hammer, to make a pair of tongs out of wood, and to put together other such tools as the need arose. Thus prepared, he would not immediately attempt to forge

26

Cf. Marion 1981: p. 77. Lojacono 1996a. 28 Regulae ad directionem ingenii, VI, AT X 381–382. Cf. Savini 2008. Marion 1974. 29 Regulae ad directionem ingenii, VII, AT X 391. Cf. Verbeek 2021. 30 Regulae ad directionem ingenii, X, AT X 404–405. 27

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swords, helmets, or other iron implements for others to use; rather he would first of all make hammers [. . .] for his own use [. . .] we have managed to discover only some rough precepts which appear to be innate in our minds rather than the product of any skill. (Regulae ad directionem ingenii, VIII, AT X 397, CSM I 31)

This text presents several important features. The most evident is that the first step in finding true knowledge is to make the tools one needs to discover it. Like a blacksmith who does not make a sword first but rather makes his hammer and anvil, one first needs to make the tools that one later uses in the pursuit of scientific knowledge. Yet, what underlies this is that the instructions to make the tools lie within both the method and the mechanical craft and cannot be taught by someone else. The ability to make them thus lies within the subject, and in the case of method, crafting the tools of knowledge belongs to the activity of our minds.31 While Descartes uses this example to suggest moving in knowledge step by step, this also reveals that knowledge belongs to the mind, and not to some other acquisitions—the reference is to Scholastic logic, syllogism, and collections of opinions from books. Later in Rule 8, Descartes also stresses that “the intellect alone [. . .] is capable of scientia, [scientific knowledge]” and that one deals with the knowledge of things “only in so far as they are within the reach of the intellect” (Regulae ad directionem ingenii, VIII, AT 398–399; CSM I 32). In restricting knowledge to the perimeter of reason, Descartes affirms that one should then “seek to encompass in thought everything in the universe, with a view to learning in what way particular things may be susceptible of investigation by the human mind” (Regulae ad directionem ingenii, VIII, AT 398; CSM I 31).32 The diversity and scattered condition of the particular things of nature become the object of knowledge insofar as they can be encompassed within the order of reason, according to Descartes. The goal of the method is to apply the order of knowledge (mental cognition) to the diversity of nature, reducing the latter to the former. In Discours de la Méthode, he describes this epistemology by means of biography. A decisive moment in the foundation of scientia occurred as he was in Germany and “stayed [. . .] in a stove-heated room, where [he] was completely free to converse with [him]self about [his] own thoughts” (Discours de la Méthode II, AT VI 11; CSM I 116). In contrast to the rich and multifaceted system of the Scholastics, established on the accumulation of books, diverse authorities, and syllogisms, Descartes freed himself from any distractions, and “resolved [. . .] to undertake studies within [him]self [. . .] and to use all the powers of [his] mind” (Discours de la Méthode II, AT VI 10; CSM I 116). As in the Regulae, Descartes claims that knowledge is a construction of reason, and in this sense, it is an individual enterprise aiming at “attaining the knowledge of everything within my mental capabilities [mon

Regulae ad directionem ingenii, VIII, AT X 397, CSM I 31: these “rough precepts [. . .] appear to be innate in our minds rather than the product of any skill.” Cf. Dika 2023: 154. 32 Original Latin is: “Neque immensum est opus, res omnes in hac univeritate contentas cogitatione velle complecti, ut, quomodo singulae mentis nostrae examini subjectae sint, agnoscamus.” 31

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esprit serait capable]” (Discours de la Méthode II, AT VI 17; CSM I 119). The first rule consists in accepting only evident knowledge, that is “what presented itself to [the] mind so clearly and distinctly that [there is] no occasion to doubt it” (Discours de la Méthode II, AT VI 18; CSM I 120), therefore grounding knowledge on the intellectual evidence of clear and distinct ideas. Yet, Descartes adds something fundamental. Accordingly, in practicing the method, one feels the “mind gradually becomes accustomed to conceiving its objects more clearly and distinctly; and since [one does] not restrict the method to any particular subject-matter, [one may] apply it as usefully to the problems of the other sciences as [. . .] to those of algebra” (Discours de la Méthode II, AT VI 21; CSM I 121). As a matter of fact, reducing the object of knowledge to the order of reason consists of conceiving it through ideas (similarly to what happens with mathematics). In this way, one may acquire a certain and evident knowledge of all natural bodies. While this rational systematization of knowledge appears well-rounded and omni-comprehensive, difficulties, however, surface in Part 6 of the Discours, as Descartes claimed to have faced serious problems when descending to more particular things. Accordingly, “the human mind could [not] possibly distinguish the forms or species of bodies that are on the earth from an infinity of others that might be there . . .” (Discours de la Méthode, VI, AT VI 64; CSM I 144). Although earlier in the Discours and previously in the Regulae Descartes had claimed it possible for the mind to encompass all particular bodies, at this stage, a restriction to the power of reason significantly emerges, uncovering a crucial gap between the reason and nature. In order to fill this gap, experimentation arises as a crucial feature to complete the knowledge of particular bodies. In the next sections, I explore this issue.

2.2 2.2.1

A Method of Experiments: The Regulae and the Correspondence of the Early 1630s Experiments and Method in Descartes’s Epistemology

Despite the rational basis of Descartes’s epistemology,33 scientific knowledge is not just a rationally pure enterprise. This surfaces already in the Regulae. The confrontation with objects mediated through experience represents a decisive step in constructing science, especially in diverse fields of knowledge. Besides the claim that knowledge is an actual grasp of the mind, in the Regulae, Descartes distances himself from “those philosophers who take no account of experience and think that truth will spring from their brains like Minerva from the head of Jupiter” (Regulae ad directionem ingenii, V, AT X 380; CSM I 21). Since the work of Desmond Clarke,

33 Notoriously, sensible knowledge is inadequate, confused, and obscure, as Descartes opposed intellectual knowledge to it.

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setting aside the anachronistic distinction between experimentalism and rationalism is crucial to understand Descartes’s method in its entirety.34 In Descartes, experimentation became fundamental in clarifying knowledge in the mental investigation of particular bodies,35 and therefore in constructing his natural philosophical program. In Rule 2 of the Regulae, Descartes acknowledges “two ways” to achieve “the knowledge of things: through experience, or through deduction” (Regulae ad directionem ingenii, II, AT X 365; H 75). However, while deduction “can never be performed wrongly,” he claimed that “our experiences of things are often deceptive” (Regulae ad directionem ingenii, II, AT X 365; H 75). This deception depends on “the fact that certain hardly understood [intellecta] observations are taken for granted or that judgements are made rashly and groundlessly” (Regulae ad directionem ingenii, II, AT X 365; H 75). Accordingly, mistakes result when experiments are detached from intellectual certainty. Rather, one should ground experimentation in the order of reason as a way to perform sound experiments and avoid the risk that experience renders knowledge uncertain. In order to do so, he transports the certainty of reason onto experiments,36 encompassing the latter within the mind’s intellectual powers, which regulate all the diverse steps of experimentation. In other words, any experiment should respond to a theory. From Rule 5, he explains the methodical activity of reason on experience. While in the text of Rule 5 Descartes describes the method as an activity of the mind, in the explanation of the rule, he stresses that following an order in knowledge means for astrologers to “make any accurate observations of celestial motions” and for philosophers to “take [. . .] account of experience” (Regulae ad directionem ingenii, V, AT X 380; CSM I 20–21). The importance of experimentation on the path to knowledge cannot be overstated. Still, understanding how performing experiments or gathering observations fits with a method established on intellectual operations remains difficult to grasp in its entirety. An epistemological explanation to clarify this connection surfaces in the following rules, as Descartes describes the disposition in series, comparisons, proportions between physical magnitudes, reviews of data, enumerations and induction of bodies, traditionally belonging to the context of experimentation, as methodical procedures. In Rule 6, he presents the arrangement in series. Accordingly, “all things can be arranged serially in various groups, not in so far as they can be referred to some ontological genus (such as the categories into which philosophers divide things), but in so far as some things can be known on the basis of others” (Regulae ad directionem ingenii., VI, AT X 381; CSM I 21). The arrangement in series thus belongs neither to a Scholastic categorization, nor to the experience of things, but to the cognitive order. When investigating anything, instead of defining their singular

34 See Clarke 1982. Hatfield 1988. Garber 2000. Charrak 2009. Dobre and Nyden 2013. Bos and Verbeek 2013. Cassan 2014. Baldassarri 2017. Sgarbi 2023. 35 For instance, see Larmore 1980. 36 Cf. Marion 1981, p. 43.

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nature, the method operates in setting things in an orderly manner or in a proportion established by reason. This order consists in the intellectual definition of the simple nature, the absolute or relative, or the ratio of a proportion, the point of departure of knowledge. The mind thus regulates this methodical procedure entirely. Yet, Descartes expands his investigation on the ways one acquires data. He claims that the same methodical process of arranging in series and proportions works both for the purely rational things (such as numbers), which are subjects of intuition, and for the data of experimentation. Indeed, since only a few things can be “intuit[ed] straight off and per se (independently of any others),” he stresses that also “sensory experience” (Regulae ad directionem ingenii, VI, AT X 383; CSM I 22) provides the data for the arrangement in series. In either case, namely while dealing with data directly intuited or with data provided by experimentation, the method operates by making arrangements of bodies following the order of reason. In fact, one must “distinguish [between objects] with [. . .] the sharp edge of our mind, [and one] must seek a means of developing our intelligence in such a way that [one] can discern these connections” (Regulae ad directionem ingenii, VI, AT X 384; CSM I 23) also “reflecting with some discernement on the minute details of the things [. . .] already perceived” (Regulae ad directionem ingenii, VI, AT X 384; CSM I 23). Discerning the connections between natural bodies belongs to reason, as it operates through comparisons, arrangements in series, proportions on the data of experimentation. An application of this procedure later surfaces in Rule 12, where Descartes repeats that intuition also operates on the experience of material bodies, making it intelligible.37 Any arrangement of bodies is, thus, an operation of a rational order. In Rule 7, Descartes suggests a methodical operation to survey every single body and include it within enumerations. Accordingly, one gathers diverse objects in enumerations, producing a set of diverse things, or collecting items in a way that “nothing [would] escape” (Regulae ad directionem ingenii, VII, AT X 388; CSM I 25) and induction operates by uncovering an underlying connection, reducing these collected or multifaceted qualities to a singular feature, “infer[ring] one thing [unum quid] from many disconnected things” (Regulae ad directionem ingenii, VII, AT X 389; CSM I 25 [translation slightly modified]) and “simultaneously intuiting one relation and passing on to the next, until I have learnt to pass from the first to the last [. . .] and I seem to intuit the whole thing at once” (Regulae ad directionem ingenii, VII, AT X 388; CSM I 25) ultimately reducing these varieties to classes of intellectual evidence.38 As Theo Verbeek has recently outlined, Descartes’s enumeration is an analytical process, in which knowledge belongs to the intellectual ability to discover a hidden connection between bodies.39 This connection is rationally established. For instance, by means of enumeration and induction, one may know something about an object E, that is not immediately related to object A, on which one has already acquired true knowledge. The discussion of the sensitive herb

37

Regulae ad directionem ingenii, XII, AT X 419–420; CSM I 44–45. Regulae ad directionem ingenii, VII, AT X 391; CSM I 27. On induction, see also Will 1974. 39 Verbeek 2021: pp. 53–55. See also, Dika 2023: 93–109. 38

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reveals an application of this procedure, as Descartes tested the validity of the animal-machine model for the knowledge of plants in general, while he isolated a point of convergence between the animal-machine model and this plant.40 Similarly to the arrangement in series, in this procedure one should apply the operations of the intellect to systematize and order the data from observations. In this sense, while what results from experimentation surfaces as a helpful means to “make our knowledge [scientia] complete” (Regulae ad directionem ingenii, VII, AT X 387; CSM I 25) providing the details of natural objects, namely their qualities, forms, and so on, the methodical procedures reduce these data to intelligibility—Descartes provides further examples of this methodical application on experimentation in Rules 8, 9, 10, and 11, as he discusses several case studies. In Rule 12, he explores from a physiological perspective the relation between intellectual knowledge, sensation, memory, and imagination, which were kept apart in Rule 3. Accordingly, during sensation, we receive a nervous impulse of the thing we observe or experience, which takes a specific shape in the nerves.41 This point is consistent with Descartes’s rejection of the Aristotelian theory of substantial forms and results in the definition of a new theory of representation, where ideas represent things without any need for visual resemblance, but mostly by means of geometry and mechanics.42 Accordingly, in sensation, there is no entity really passing from the external object to the sense organ, as it was for Aristotelian tradition, but the object hitting the senses produces a nervous impulse that reaches the brain, where it is transformed into a geometrical figure; as Descartes writes, “when an external sense organ is stimulated by an object, the figure which it receives is conveyed [. . .] to another part of the body known as the ‘common’ sense, without any entity really passing from the one to the other” (Regulae ad directionem ingenii XII, AT X 414; CSM I 41).43 Descartes describes this point by means of the famous example of colors—previously described in the introduction of this book. Following this moment, the common sense fashions the figure in the phantasy or imagination, borrowing from mechanics the mathematical modelling of natural bodies, ultimately reducing the qualitative aspects of the material bodies one observes in nature to a geometrical figure in the mind.44 This consists of producing an idea of the object.45

40

Verbeek 2021: p. 55. See Chap. 5 of this book. Regulae ad directionem ingenii XII, AT X 412–413; CSM I 40: “sense perception occurs in the same way in which wax takes on an impression from a seal [. . .]. The same is true of the other senses: thus, in the eye, the first opaque membrane receives the shape impressed upon it by multicoloured light [. . .] the concept of shape is so simple and common that it is involved in everything perceivable by the senses.” See Garber 1992. 42 Hattab 2009. Crifasi 2011. Sepper 2013. Cf. Wolf-Devine 1993. 43 On the role of geometry, see also Rabouin 2021. 44 In Aristotelian tradition, this appeal to a mathematical modeling, reducing natural bodies to geometry, was conceived as an error. See Funkenstein 1986: pp. 299–326. 45 Regulae ad directionem ingenii XII, AT X 416–417; CSM I 43: “the intellect proposes to examine something which can be referred to the body, the idea of that thing must be formed as distinctly as possible in the imagination.” Although I am not going to deal with the Meditationes, my impression 41

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Knowledge thus consists of a reduction of natural bodies to a geometrical figure, and the power regulating this process ultimately resides in the mind, as “the power through which we know things in the strict sense is purely spiritual” (Regulae ad directionem ingenii XII, AT X 415; CSM I 42). Reducing the object perceived or observed in physics to an intellectual pattern reveals the ways the mind regulates experimentation, ultimately making particular bodies intelligible by means of a mathematical model. In this sense, the mind embeds particular bodies within a cognitive order, conceiving their qualities within a mathematical systematization. The Discours summarizes the same relationship between the method and experiential data, from a diverse perspective, as the epistemological organization of the Regulae leaves room for a more practical description of the method. While the four rules of his method present a rationalistic systematization, there are some important features related to experimentation. In Rule 3 of the Discours, Descartes affirms that one should investigate the objects of nature, opening to the knowledge from the effects. In the first part of this rule, Descartes claims that one should follow a deductive chain, directing thoughts from the simplest to the most complex bodies, that is, from the cause to the effects. This is a priori knowledge and follows the thread of causation, which is rationally framed in Descartes’s philosophy.46 Yet, he completes this rule with the necessity to “suppos[e] some order even among objects that have no natural order of precedence” (Discours de la Méthode II, AT VI 19; CSM I 120). Accordingly, deduction may also work in the other direction, dealing with effects and without moving from their causes, or supposing a cause or an order where there is apparently none. The reason constructs such an order and isolates the point of departure for the thread of causation, as the power of the mind grounds suppositions and hypotheses. In this case, knowledge has an a posteriori structure, moving from the variety or diversity of effects perceived or observed, when the natural order is not evident. Yet, this supposition is rationally established. This case surfaces in Descartes’s medicine, for L’Homme starts with a supposition grounded on several observations, as he moved from a specific point of the structure of living bodies (the heartbeat), and not from the beginning of life (embryology). From this supposition, he designed a theoretical model (the animal-machine), which he tested throughout the text by means of anatomical observations and physiological reconstructions, ultimately deducing some physiological truths from it.47 In Rule 4 of the Discours, Descartes claims that one should “make enumerations so complete, and reviews so comprehensive [to avoid] leaving anything out” (Discours de la Méthode II, AT VI 19; CSM I 120). When the object of knowledge is complex, enumerations are necessary to help deduction. As he stresses some pages is that this does not differ from the knowledge of wax in Meditatio II, whose nature is known by an act of the intellect. Nonetheless, “the wax remains,” as Descartes claimed. See Wild 2024. 46 Cf. Carraud 2002. 47 Discours de la Méthode, V, AT VI 45–46; CSM I 134: since “I did not yet have sufficient knowledge to speak of them in the same manner as I did of the other things—that is, by demonstrating effects from causes [. . .] I contented myself with supposing [. . .]. I supposed, too . . .” On Descartes and medicine, see Baldassarri 2021a. Baldassarri 2022a.

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later, one should gather “a variety of experiences to serve as the subject-matter of [their] reasonings” (Discours de la Méthode II, AT VI 22; CSM I 122). In this sense, experimentation provides Descartes’s method with data to fill scientific knowledge, therefore helping reason to achieve knowledge. Experimentation and reason are not detached, as the methodical procedures connect these features. In sum, scientific knowledge surfaces as a combination of intuition and deduction (a priori knowledge), with hypotheses, experimentation, and enumerations (a posteriori knowledge), methodologically organized.48

2.2.2

Reason and Experience in the Correspondence with Beeckman: A Battle for Scientia

A further investigation of this connection surfaces in Descartes’s early 1630s correspondence, when he debated his conception of science as knowledge grounded in the order of reason, especially dealing with their various ways of performing experimentation.49 On the one hand, Descartes challenged the un-methodological attempts to attain knowledge by peer scholars such as Beeckman and Mersenne, while on the other hand, he proposed his own methodical systematization of experimentation. The correspondence thus appears as a laboratory to explore the application of his method in the sciences. The October 1630 letter to Isaac Beeckman is a touchstone in Descartes’s definition of science. This is the result of a shaky relationship, developing from Beeckman’s claim to be the true inventor of Descartes’s mathematical and musical theories.50 Yet, Descartes’s argument develops from a moral issue (i.e., one should not steal a friend’s work) into a diagnosis of a bad state of mind: Since Beeckman claimed to be the author of Descartes’s inventions, he should be ill, according to Descartes. The remedy is related to the epistemological definition of knowledge as an act of reason in which the mind heals itself. Against Beeckman’s authoritative behavior, Descartes opposes his own method of discovery. Moving from the example of what one could learn from teachings, Descartes differentiates between the disciplines such as “language, history, experiments, and thus also the demonstrations certain and manifested, like those of geometers [. . .]” and “philosopher’s aphorisms and opinions [that] cannot be taught only because someone had affirmed them” (Descartes to Beeckman, October 17, 1630, AT I 158; 48 Cf. Gaukroger 1989: Chap. 3, “Discovery and Proof,” pp. 72–102. See also Shapiro 1983: p. 45: “hypotheses were derived a priori from the principles of Cartesian physics. Experiments might help decide between alternate a priori ways of ‘deducing’ phenomenon to be explained, but the hypotheses themselves were not derived from experiment or observed data.” 49 For a detailed reconstruction, see Schuster 2013 and Schuster 2022. 50 Cf. Descartes to Beeckman, October 17, 1630, AT I 159–160; CSM I 27. Descartes to Mersenne, November 4, 1630, AT I 171–172. Descartes to Mersenne, November 25, 1630, AT I 176–178. Cf. van Berkel 2000. Arthur 2007. Cf. Sepper 1996: pp. 59–61.

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CSM I 26 [translation slightly modified]). The difference lies in the fact that the first “persuade the mind” (Descartes to Beeckman, October 17, 1630, AT I 158; CSM I 27) as one acquires knowledge through an activity of reason, while beliefs in authority do not produce any knowledge, according to Descartes. As a result, knowledge does not belong to the accumulation of information. After having dismissed any tutoring role by Beeckman, Descartes provides a list of three kinds of discoveries [tria genera inventorum]. The first is realized by the strength of the ingenium and led by reason alone [quod solius ingenii vi et rationis ductu], the second through luck [non ab ingenio venit, sed a fortuna], the third in awarding significance to useless things [cum nullius aut perexigui sint valoris, ab inventoribus . . . magnae res aestimantur].51 The first belongs to reason and grants true knowledge (scientia), while the other two do not. Grounded on the definition of scientific knowledge as an activity of reason, Descartes opposes his methodology for acquiring knowledge to Beeckman’s, which consists in gathering and performing experiments as noted in his Journal and ordering them through a Mathematico-physics system. Descartes mischaracterizes Beeckman’s method as a mere accumulation and repetition of the notions or experiments of someone else.52 Despite carefully and painstakingly organizing experiments through his physico-mathematics, Descartes conceived of Beeckman’s notes as too scattered and fragmented to achieve true knowledge. In contrast, knowledge is a grasp of one’s own reason. Moreover, in stressing that Beeckman’s Journal is only a work of collecting information and notions, Descartes advocates that singular notions (such as experiments, observations, or collections of data) do not yield any actual knowledge when considered by themselves—he claims that the only value of the Journal lies in its binding, an unjustifiable criticism. In this letter, he misrepresents Beeckman’s collection of experimentation as of little use, for he had collected them without any (cognitive) order, that is, without any theory, and his criticism matches his challenges to history as a collection of data. In contrast, Descartes lays bare that true knowledge results from a theory, and singular experiments need to be connected to principles. A theoretical framework should therefore guide experimentation. This connection is clarified in another letter to Beeckman of 1634. While discussing the speed of light, their opposing emphases on experimentation surface. As Descartes fleshes out, Beeckman based his explanation on a terrestrial observation he performed with a torch and a mirror, inferring that the light is not instantaneous by the qualitative observation of its motion. Descartes additionally remarks that Beeckman borrowed the experiment from Bacon’s Sylva sylvarum,53 despite

51

Descartes to Beeckman, October 17, 1630, AT I 160–162. Ibid., AT I 159; CSM I 27. Descartes compared Beeckman’s methodology to the Batrachomyomachia, a Greek parody of the Iliad, titled Battle of Frogs and Mice. 53 Cf. Bacon, Sylva sylvarum, 209, SEH II, p. 416. Beeckman, Journal, III, p. 49, 54. On Beeckman’s interest in Bacon’s experimentation, see Gemelli 2013. Gemelli 2014. 52

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deriving the opposite conclusion from Bacon’s.54 According to Descartes, Beeckman concentrates too much confidence in experimentation [experimento confidebas], neglecting to combine this to a theory of light, while he himself performed an experiment that is consistent with a theory. Descartes proposes the common experience of looking at the sky during an eclipse (which has been done by thousands of people and by astronomers),55 stressing that the astronomical distances would make perceptible the time of the light—if any—because a temporal difference would emerge between the timing of the eclipse and the time the observer saw it. Yet, Descartes reduces this astronomical set to a geometrical model and a computation of the timeframe within which the observer would see the light. If there were a delay, the Sun and the Moon would not be seen on the same line (where they theoretically had to be), and there would be a difference of an hour between the eclipse and its observation.56 Still, Descartes does not infer the instantaneity of light from this observation but uses this case to confirm his theory of light. The ground is the intuition developed in the Regulae that a natural power is instantaneous and that, according to his definition of motion, it moves rectilinearly. Since light is a power, it should be instantaneous, and the transmission of light is rectilinear.57 The astronomical observation confirms these intuitions: During an eclipse the Sun, the Moon, and the Earth should lie on a rectilinear line, making the eclipse effective, but this is possible only with the instantaneity of light, otherwise a difference of seconds would be perceptible, and the celestial bodies would not align, and in this sense, there would be no eclipse.58 Consequently, this observation confirms that the transmission of light is rectilinear, ultimately confirming the instantaneity of light. While both Descartes and Beeckman referred to two observations to set the dispute over the speed of light, an outstanding difference arises. Beeckman’s mostly relies on the sensory understanding of what one observes, and as a result he is forced to collect as much data as possible, failing to produce any systematicity—according to Descartes’s criticism. In contrast, Descartes grounds his knowledge in the principles of his physics—namely the instantaneous transmission of natural power, his theory of light, and ultimately his theory of matter. When observing a phenomenon, Descartes reduces it to a geometrical order and seeks confirmation for his theory.

54

Bacon, Novum organum, II, OFB XI, 46, pp. 376–378. Beeckman, Journal, II, p. 253. Descartes was aware of Kepler’s argument that the light emitted at a point A would be seen instantly at a point B even though the distance between A and B was astronomical. 56 Descartes to Beeckman, August 22, 1634, AT I 310. 57 On the instantaneity of a natural power, see Regulae ad directionem ingenii IX, AT X 402; CSM I 34. On light, see Le Monde V, AT XI 24–25, 26; CSM I 89. On the rectilinear transmission of light, see Le Monde IV, AT XI 99–100: “Quant à ce qui est des lignes [. . .] qui sont proprement les rayons de la Lumière [. . .] les concevoir exactement droites.” Cf. La Dioptrique, AT VI 84–85; CSM I 153. See also Dika 2022: 428–429. 58 Descartes to Beeckman, August 22, 1634, AT I 312. Descartes also represented the linearity between bodies. 55

2.2

A Method of Experiments: The Regulae and the Correspondence of the Early 1630s

37

In Descartes’s epistemology, experiential data are framed within reason, namely within a mathematical system and within the principles of physics, which encapsulates the data of observation, providing certainty to knowledge.

2.2.3

Mersenne and Descartes: Lists of Qualities, Useful Experiments, and Natural History

In this way, experimentation is made useful. This is the subject of his 1630s correspondence with Mersenne. While he repeats the epistemology of the Regulae, according to which all scientific explanations come from reason,59 for intuition knows the principles of physics, it also articulates the ways reason frames experiments and observations.60 In discussing observations, lists of qualities, and natural history with Mersenne, Descartes expounds what makes them useful tools for knowledge. In a January 1630 letter to Mersenne, he writes: I thank you for the [list of] qualities you have drawn from Aristotle. I have already taken another and bigger list, partly from Verulam [i.e., Francis Bacon], partly from my reason [de ma tête]; and this is one of the first things I am willing to explain without many difficulties, as we would retain, for when foundations are laid, [the explanation of qualities] easily follows (Descartes to Mersenne, January 1630, AT I 109 [translation is mine]).

Accordingly, lists of qualities usefully help capture the vastness of nature and provide deduction with data. Then, Descartes adds that explaining the qualities of bodies follows the definition of the foundations of knowledge, that is, the knowledge of principles. In this sense, a theory is required to make the lists of qualities useful— and one could equally draw these lists from Aristotle or Bacon. This is partly what he did in Le Monde, where he reduces secondary qualities to the extension alone,61 that is, to the principles of physics.62 While explaining qualities, he orders them by means of the geometrical and mechanical model of his philosophy. In a letter of December 23, 1630, while answering Mersenne’s request for a system to make useful experiments, Descartes proclaims that: “[w]ith regards to this I have nothing to say, after what Verulam [i.e., Bacon] wrote” (Descartes to Mersenne, December 23, 1630, AT I 195 [translation is mine]).63 And then he adds that:

59

Descartes to Mersenne, October 8, 1629, AT I 22; CSMK 6. Descartes to Mersenne, April 15, 1630, AT I 144; CSMK 22. 61 Chapter 2 of Le Monde is on heat and fire, Chap. 3 of Le Monde is on hardness and flexibility, and in Chap. 5 of Le Monde all qualities are reduced to extension, movement, and figure. See Verbeek 2000. What exactly Descartes read of Bacon is unknown, though he probably referred to the De Dignitate et Augmentis scientiarum, III, 4, 560. See also Petrescu 2015. 62 Le Monde, V, AT XI 37. 63 On Mersenne and Bacon, see Buccolini 2013. Buccolini 2014. 60

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without being too curious in looking for all small particulars in every field, it is mostly necessary to have general gatherings about the most common things, the most certain, and the simplest to know: i.e., whether the coil of shells is turned in the same way [. . .]. Whether the animal body is sorted in three parts, caput, pectus et ventrem [. . .]; since these are infallibly needed for the search for truth. For the most particular, it is impossible to avoid unnecessary and also false experiences, without possessing the truth of things before doing them. (Descartes to Mersenne, December 23, 1630, AT I 195-196 [translation is mine])64

Besides Descartes’s unexpected designation of Bacon as a suitable example to devise useful experiments, in this letter, he significantly presents two kinds of observations. The first concerns general gatherings about very simple things, while the second concerns the observation of more particular objects. Accordingly, the former are necessary in the search for truth, while the latter could lead to unnecessary and false experiences or experiment, therefore to false knowledge. Useless or false experiment are a recurring topos in Descartes’s correspondence,65 but here he makes the epistemological assumption that one should know the truth before performing any investigation in order to avoid false experiment—he applied this feature in the discussion about the speed of light. In Cartesian epistemology, knowledge is an actual grasp of reason, as one intuits truth and then deduces several inferences from it, and this is not a mere attempt to discover an ungrounded truth. In this sense, experimentation serves to confirm a theory already grasped. Yet, Descartes differentiates between experiments concerning common things and those concerning particular objects. Accordingly, the first are useful, as they provide reason with general data of nature that one could reduce into a pattern, while the second only concerns very particular bodies, and it is difficult to draw a systematic knowledge of nature from them. A useful experiment or observation is one that helps in defining a relationship between things, ordering them in a geometrico-mechanical pattern.66 The latter operation is much more difficult when dealing with particular things, such as the object of curiosity. Although Descartes does not specify what he means exactly, he likely refers to the objects of natural historical collections, or the widespread attraction to rare and very particular bodies, which also concerned

64 While the first request belongs to daily experience, the second expresses the Aristotelian division of the body to locate the different parts or organs by which anatomical science was accomplished. Harvey started his lectures with such historiæ, and his natural philosophy was clearly Aristotelian, but, of course, this issue presents some difficulties that I am not dealing with at this stage. Descartes inserted Aristotelian natural philosophy into a new system of science: Knowledge is no longer attained by comparing particular instances (from which to abstract a universal concept). Harvey, Lectures on the whole of Anatomy: p. 35. French 1994. Pomata and Siraisi 2005. Aucante 2006a, b. 65 See, for instance, in the case of metals, Mersenne provided Descartes with a list (cf. Descartes to Mersenne, January 1630, AT I 113, “une table”) of “observations des métaux,” judged useless (Descartes to Mersenne, February 25, 1630, AT I 122–123). See Chap. 4 of this book on this subject. See also the case of botanical catalogs, which are useless insofar as they contain names or words, instead of things. See Chap. 5 on this topic. 66 This is consistent with the epistemology of the Regulae, and specifically the operation of enumeration and induction.

2.2

A Method of Experiments: The Regulae and the Correspondence of the Early 1630s

39

Mersenne’s investigations.67 Since these bodies are too scattered, it is difficult to embed them within a theory, and reducing them to a mechanical model is more complex, if not impossible. A possible example of the difficult knowledge with particular bodies may concern the case of magnetic attraction, as presented in the Regulae: Since one cannot easily intuit the theory of magnetism, performing observations on magnets before knowing the theory is fruitless to achieve a sound knowledge.68 In a May 1632 letter, Descartes presents natural history as a significant addition to knowledge. As he writes to Mersenne, it would be very useful if someone is willing: to write the history of celestial phenomena in accordance with the methodology of Verulam; and, without inserting any arguments or hypotheses, he would exactly describe the present appearances of the heavens, reporting the position of each fixed star [. . .], listing their differences in size and colour and visibility and brilliance and so on. He should tell us how far this accords with what ancient astronomers have written and what differences are to be found [. . .]. He should add the observations which have been made of comets, with a table of the path of each like the ones Tycho [Brahe] made of the three or four that he observed, and he should include the variations in the ecliptic and apogee of planets. Such a work would be more generally useful [. . .] and it would relieve me of a great deal of trouble (Descartes to Mersenne, 10 May 1632, AT I 251-252; CSMK 38 [translation slightly modified.])

This section of the letter contains some crucial features. First of all, Descartes acknowledges the usefulness of natural history, or history of phenomena, when embracing Bacon’s methodology to achieve them. Insofar as natural history collects several data, Descartes welcomes it as a fruitful tool, as he then repeats to van Hogelande in 1640 concerning a history of mathematics.69 Indeed, such collections of data and facts provide nature as it is. Still, Descartes insists that one should make them according to a Baconian model for the collecting of items, but without adding theoretical assumptions—which, in contrast, occurs in Bacon.70 Such a natural history would consist of a description of the heavens that includes a comparison with the descriptions of the Ancients and the observations of all cosmological bodies ordered in tables—for instance, in the case of comets, this history should include a table of the path of each comet, following Brahe’s work. This enterprise would be useful to achieve a sound cosmological knowledge. At the time, Descartes was studying the heavens and had “discovered their nature and the nature of the stars we see there [. . .] and ha[d] become so rash as to seek the cause of the position of each fixed star” (Descartes to Mersenne, May 10, 1632, AT I 250; CSMK 37–38). 67

Descartes to Huygens, March 12, 1640 AT III 756. On curiosity as a disease, see Les Passions de l’âme, AT XI 383–386; CSM I 354–356. Lojacono 1990. 68 On magnetism in Descartes, see D’Agostino 2022. See also Sect. 4.5 in this book. 69 Descartes to Hogelande, February 8, 1640, AT III 723–724, CSMK 144: “It would, however, be highly desirable if the historical part of mathematics which is scattered among many volumes and is as yet incomplete and imperfect were collected wholly within a single book [. . .]. Moreover, the chief need would not be so much for diligence in collecting everything together as for judgment in rejecting what is superfluous, and knowledge to fill the gaps where previous attempts at discovery have failed.” 70 Giglioni 2012.

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This entails that he had elaborated a theory of the heavens and then needed some observations to apply his theory to the knowledge of particular, individual cases.71 From this theoretical assumptions, Descartes claims to be able to devise the cause of the position of each star, and it would be possible to describe an order in what appears “irregularly distributed in various places in the heavens,” therefore discovering “a natural order [. . .] which is regular and determinate.” Accordingly, “the discovery of this order is the key and foundation of the highest and most perfect science of the nature of things [la matérialité des choses]” (Descartes to Mersenne, May 10, 1632, AT I 250; CSMK 38). This point is crucial in Descartes’s epistemology. In fact, if one possesses this theoretical knowledge, one would know every particular body a priori, or, as he says, the nature of these bodies and therefore work out their position. This theoretical knowledge would provide nature—the sky, in this case—with a rational order that makes all bodies intelligible. However, in order to describe any individual case, observations and natural history are necessary to attain certain knowledge, as the latter provide theory with data that someone cannot know by heart.72 This combination of theory and experimentation is confirmed in an April 1632 letter to Mersenne, where Descartes had affirmed that he was “supplementing my reasoning with observations”: (Descartes to Mersenne, April 5, 1632, AT I 243; CSMK 37) theoretical principles ground scientific knowledge and observations supplement it with data—in sum, lists of qualities, observations, natural history, and tables of data appear central in Descartes’s epistemology, as a means to the advancement of the sciences. In 1635, Descartes made this point clear in an experiment regarding the weight of air that Mersenne had suggested to several correspondents, Descartes included.73 According to the latter, Mersenne’s experiment appears unsuitable for his goal, mostly because he followed an erroneous procedure, and results in a useless observation.74 Descartes thus criticizes Mersenne’s method and suggests that one should perform experiments only under the guidance of reason, i.e., having a goal and ultimately aiming to confirm or reject a theory, and not in a casual fashion—for instance, Mersenne mostly collects diverse observations, without following a precise order, according to Descartes.

71

This is the subject of Le Monde. Descartes to Mersenne, May 10, 1632, AT I 251; CSMK 38: “if we possessed it, we could discover a priori all the different forms and essences of terrestrial bodies, whereas without it we have to content ourselves with guessing them a posteriori and from their effects.” Cf. Mittelstrass 1977. See also Descartes, Second replies, AT VII 155–156; CSM II 110–111, on analysis (a priori) and synthesis (a posteriori). 73 Cf. Mersenne 1626: pp. 214–215. This belongs to Bacon, Novum organum, II, 40, OFB XI 312–315. See also, Cornier à Mersenne, November 15, 1627, CM I, 592–593. Mersenne to Rey, September 1, 1631, CM III 189. Rey to Mersenne, January 1, 1632, CM III 239–240. Mersenne to Rey, April 1, 1632, CM III 280, “je pense avoir trouvé le moyen de peser l’air.” Mersenne to Peiresc, July 15, 1635, CM V 300. 74 Descartes to Mersenne, 1635–1636, AT IV 688–689. Cf. CM V 586. 72

2.3

Observations in a System: Knowledge of Particular Bodies from. . .

41

Both in the epistemology of the Regulae and in the correspondence, Descartes diluted his rationalistic framework through an appeal to experimentation, lists of qualities, natural history, observations and a posteriori knowledge, which help confirm his theory and especially operate in the study of particular cases or individual bodies. However, the order of the mind must organize and guide experimentation, by operating on the object of experimentation and providing observations with a theory, ultimately specifying a way to perform useful experiments. As Clarke has stressed, “Descartes’ reservations about empirical evidence result from his critique of experimental techniques or the interpretation of experimental data” (Clarke 1991: 470).75 According to Descartes, experimentation helps in acquiring data on nature, while reason interprets these data, making them intelligible, physically consistent, and useful to achieve true knowledge. The more one deals with particular or complex objects, the more experimentation is necessary—but this is, undoubtedly, an important mitigation of his early rationalistic epistemology.

2.3 2.3.1

Observations in a System: Knowledge of Particular Bodies from the Discours to the Principia Method and Necessary Experiments

While the Regulae and the early correspondence contain the methodical relation between reason and experimentation, Descartes’s major works present the application of reason to experimentation in the practice of science.76 In the Discours, for example, he claimed to have substantiated his explanation of the heartbeat by means of observations and experiments.77 Yet, while Parts 1–5 of the Discours intertwine a short biography of his philosophical enterprise with his scientific investigations (such as the heartbeat in Part 5), “the sixth and final chapter of Descartes’s Discourse on Method appears to be the only place in his work where he provides a more or less elaborate theory on the use of experiment and scientific collaborations” (Bos and Verbeek 2013: 161)78 as Erik-Jan Bos and Theo Verbeek have pointed out. Probably written as a response to his Dutch peers and friends, namely Henricus Reneri and Constantijn Huygens (1596–1687), the sixth part finds Descartes situating himself in a clear Baconian perspective, insofar as experimentation was linked with making

75

Cf. Clarke 1982: 37–38, 147. Sakellariadis 1982. Cf. Lojacono 1996b. 77 Discours de la Méthode V, AT VI 50; CSM I 136: “To prevent this, I would advise them that the movement I have just explained follows from the mere arrangement of the parts of the heart (which can be seen with the naked eye), from the heat in the heart (which can be felt with the fingers), and from the nature of the blood (which can be known through observation)” [emphasis added.] 78 On the structure of the Discours, see Gadoffre 1987. 76

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one the lord and master of nature. Still, he embeds experimentation within a philosophical quest for certainty theoretically grounded. On the one hand, Descartes appeals to the authorities to support scholars to perform all the observations needed, therefore avoiding the risk of “the lack of observations,” which affects the results of the Principia, for instance. Moreover, he affirms that observations would be helpful to “make further progress” in science, as “by building upon the work of our predecessors and combining the lives and labours of many, we might make much greater progress working together than anyone could make on his own” (Discours de la Méthode, VI, AT VI 63; CSM I 143).79 Yet, in speaking of predecessors and collaborations, Descartes opens out to a system of traditional knowledge grounded in history, something previously rejected, as I have claimed earlier in this chapter.80 This position reveals Descartes’s eagerness to achieve knowledge through observations and experimentation, and it reveals a change from his early extreme rationalism. Moreover, Descartes claims that experiments (and collaborations) become important at the second stage of scientific investigation, as “the further we advance in our knowledge, the more necessary [observations and experiments] become” (Discours de la Méthode, VI, AT VI 63; CSM I 143). But then, in the Discours, he discloses a precise division of the diverse phases of knowledge, specifying when exactly experimentation is crucial, and therefore spelling out the diverse moments in the path of knowledge.81 Accordingly, one first seeks to discover “the principles or first causes of everything that exist [. . .] in the world” (Discours de la Méthode, VI, AT VI 64; CSM I 143). These are (a) God as the creator of the universe and (b) “certain seeds of truth which are naturally in our souls” (Discours de la Méthode, VI, AT VI 64; CSM I 144). The principles or first causes, or simple natures according to the lexicon of the Regulae, or laws of nature, according to the language of his physics, lie within the mind, and correspond to what one achieves through intuition. Knowledge has a rationalistic ground, at least for what concerns the basic principles. Second, one should examine “the first and most ordinary effects deducible from these causes,” i.e., those general bodies that could be easily known. In this way, Descartes “discovered the heavens, the stars, and an earth; and, on the earth, water, air, fire, minerals, and other such things which, being the most common of all and the

79

This appeal to collaborations appears in contrast to the suggestion that knowledge is an individual activity, a significant point of Part 2 of the Discours. 80 For a restriction of such collaborations, see also Discours de la Méthode, VI, AT VI 72; CSM I 148: “As regards observations which may help in this work, one man could not possibly make them all. But also he could not usefully employ other hands than his own [. . .] as voluntary helpers, who might offer to help him for curiosity or a desire to learn, usually promise more than they achieve [. . .]. And as for the observations that others have already made, even if they were willing to communicate them [. . .] they are for the most part bound up with so many details or superfluous ingredients that it would be very hard [. . .] to make out the truth in them.” 81 Descartes provided a similar reconstruction in Part 5 of the Discours, as he dealt with his physics. I will discuss this in Chap. 3 of this book.

2.3

Observations in a System: Knowledge of Particular Bodies from. . .

43

simplest, are consequently the easiest to know” (Discours de la Méthode, VI, AT VI 64; CSM I 144). The knowledge of these general bodies is the first step into the science of nature, which is knowledge a priori (from causes to effects). Third, in descending “to more particular things, [he] encountered such a variety that [. . .] the only way to making these bodies useful to us was to progress to the causes by way of the effects and to make use of many special observations” (Discours de la Méthode, VI, AT VI 64; CSM I 144). Descartes differentiates between bodies in general, such as stars or planets, and general matter composing bodies, on the one hand, and bodies in particular, which are called mixed or composite, and are composed of diverse matter, on the other hand. Several particular experiments are necessary to know these individual bodies, as one should proceed to the cause through their effects, therefore following an a posteriori path.82 Fourth, one should review in the mind the object-matter of knowledge. While these particular bodies “have been present to [the] senses,” Descartes claimed to be able to “explain [them] quite easily by the principles” (Discours de la Méthode, VI, AT VI 64; CSM I 144) of his natural philosophy, insofar as he could include them in a complete enumeration. In this way, it would be possible to deal with particular objects. This order of knowledge reflects the four rules of his method.83 Accordingly, the first consists in defining the principles or causes (by intuition), establishing the theoretical frame and grounding a priori knowledge; the second consists in deducing general effects from these causes; the third consists in inferring more particular phenomena, reshaping the thread of causation and moving from effects back to causes (this is a posteriori knowledge); and the fourth consists in enumerating the data of knowledge. As we have seen, all the four moments are regulated by the power of the mind, which makes them operative. Then, Descartes affirms that, although “the power of nature is so ample and so vast, [. . .] these principles [are] so simple and so general” that “hardly any particular effect [cannot] be deduced from the principles in many different ways” (Discours de la Méthode, VI, AT VI 64–65; CSM I 144). Here, Descartes reacts to the existence of individuals or particular bodies that are apparently irreducible to the order of reason. Although connecting any particular effect to its cause may be difficult, for there are too many or too scattered bodies, the “greatest difficulty is usually to discover in which of these ways [the knowledge of effects] depends on [the principles]” (Discours de la Méthode, VI, AT VI 65; CSM I 144). In order to find a better way to connect effects to causes, he suggests performing observations. This is a crucial point. Not only does experimentation provide knowledge with the data of nature, but also, as Garber has pointed out, observations “help us find the right deductions, the ones that pertain to our world and to the phenomena [. . .]. In this way, experiments seem not to replace deductions, but to aid us in making the proper deductions”. (Garber 1993: 293–294 [emphasis in the text]) Experimentation thus helps in

82 83

Cf. Clarke 1992. Garber 1996a. On the question of order in Descartes, see Guéroult 1953. Equipe Descartes 1979. Becco 1979.

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directing deduction. What follows is that the intellectual operations, intuition, and deduction construct the theoretical framework of knowledge, identifying principles and causes, while experimentation aids not only in connecting effects to causes but also in directing deduction when moving from an effect to the right cause. The application of this connection surfaces in the Essais, where knowledge of specific phenomena reveals a combination of deduction and experimentation. As expounded by Garber, the case of the rainbow perfectly shows the role of experimentation within Descartes’s methodology, in which observation serves to clarify the connections between particular points in the deductive chain, making clear which path deduction might follow to connect a particular effect or phenomenon to its causes.84 Still, in balancing an a priori system grounded in reason with the a posteriori knowledge produced by observations, Descartes appears forced to introduce suppositions, as he does in the Essais.85 While suppositions borrow contingency for knowledge, this latter appears merely hypothetical. In claiming that one should proceed to the causes from the effects with the help of experimentation, Descartes seems to suggest that science must become a posteriori and that principles fail to ground the knowledge of nature—it is to be noted that he did not provide his principles in the Discours. This opens out to questions the first readers of the Discours raised against Descartes.

2.3.2

A Priori and A Posteriori: Method and Experiment in the 1638 Correspondence

Challenges to Descartes’s systematization of knowledge surface in his 1638 correspondence, as scholars raised questions about the relationship between reason and experimentation, the chain of causation, and the connection between a priori and a posteriori knowledge. In the 1638 letter to Vatier, Descartes discusses the uses of hypotheses in his physics. In speaking of La Dioptrique and Les Météores, Descartes recognizes that he has grounded his explanation on several hypotheses, insofar as he “cannot prove a priori the assumptions [he] made at the beginning of the Meteorology without expounding the whole of [his] physics.” Yet, he adds that “the observational data which [he] has deduced necessarily from them, and which cannot be deduced in the same way from other principles, seem to me to prove them sufficiently a posteriori” (Descartes to Vatier, February 22, 1638, AT I 563; CSMK 87). The point is that, since the Essais only present a part of his physics, he refrains from

84 Cf. Garber 1993: 301. Garber 2001: 94: this knowledge cannot be achieved “on the basis of the seeds of truth alone.” 85 Discours de la Méthode, VI, AT VI 76; CSM I 150: “should anyone be shocked at first by some of the statements I make at the beginning of the Optics and the Meteorology because I call them ‘suppositions’ and do not seem to care about proving them . . .”

2.3

Observations in a System: Knowledge of Particular Bodies from. . .

45

dealing with the metaphysical and physical principles here, but only discusses some phenomena, which he explains moving from suppositions and by means of experimentation. As he affirms, “it is not always necessary to have a priori reasons to convince people of truth” (Descartes to Vatier, February 22, 1638, AT I 563; CSMK 87). Then, he claims that “my thought are so interconnected [la liaison de mes pensées] that I dare to hope that people will find my principles [. . .] are as well proved by the consequences I derive from them [i.e., the assumptions] as the borrowed nature of the moon’s light is proved by its waxing and waning” (Descartes to Vatier, February 22, 1638, AT I 564; CSMK 88). This letter contains some important features. The most relevant is the possibility to discover the principles moving from suppositions and hypotheses, that is, moving back from effects to causes, insofar as the method (specifically, Rule 3) provides a role for suppositions in knowledge. This is possible by means of experimentation, for the data of observations prove that an effect could be deduced from a principle. Indeed, as he has written in the Discours, “my reasonings [are] so closely interconnected that just as the last are proved by the first, which are their causes, so the first are proved by the last, which are their effects” (Discours de la Méthode, VI, AT VI 76; CSM I 150).86 Another problem, however, follows. In July 1638, he replied to Jean-Baptiste Morin (1583–1656),87 a professor of mathematics at the Collège de France with an interest in natural philosophy, who had challenged Descartes about the circular logic implicit in his attempt to prove the effects from a cause and then to prove the cause by the same effects.88 Despite agreeing with the correspondent on a few aspects, Descartes dissents on the fact that: it is circular to explain effects by a cause, and then prove the cause by the effects; because there is a big difference between proving and explaining [. . .] there is nothing circular in proving a cause by several effects which are independently known, and then proving certain other effects from this cause [. . .] and explained [this] when I said that experience renders most of these effects quite certain and so the causes from which I deduce them serve not so much to prove them as to explain them—indeed it is the causes which are proved by the effects. (Descartes to Morin, 13 July 1638, AT II 198; CSMK 106)

This letter has been importantly analyzed by interpreters. Descartes differentiates between providing proof and explanation, the first is an act of discovery, while the second only has an explanatory role. Yet, as a transition develops from proving to explaining, experience plays a central role, ultimately making the effects certain, according to Descartes. Experience is thus essential in the scientific enterprise, especially in finding the right cause. This happens not because many effects can be generated by many causes, but because through experience one discovers that a 86

Cf. Garber 1996a: 347–353. Brissey 2012. On Morin, see Garber 1988. Garber 2001: “J.-B. Morin and the Second Objections”, 64–84. 88 Morin to Descartes, February 22, 1638, AT I 529. Cf. Discours de la Méthode, VI, AT VI 76; CSM I 150: “It must not be supposed that I am here committing the fallacy that the logicians call ‘arguing in a circle.’ For as experience makes most of these effects quite certain, the causes from which I deduce them serve not so much to prove them as to explain them; indeed, quite to the contrary, it is the causes which are proved by the effects.” 87

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particular cause refers to that particular effect and vice versa, as noted by Marco Sgarbi.89 Yet, this experience is not detached from a rational order. Later in the letter, Descartes claims that he has been able to succeed where natural philosophers had failed, because he tried “to imagine some causes to explain the phenomena of nature” (Descartes to Morin, 13 July 1638, AT II 199; CSMK 107). Within this line, he then suggests Morin that: [c]ompare my assumptions [suppositions] with the assumptions of others. Compare all their real qualities, their substantial forms, their elements and countless other such things with my single assumption that all bodies are composed of parts. This is something which is visible to the naked eye in many cases and can be proved by countless reasons in others. All that I add to this is that the parts of certain kinds of bodies are of one shape rather than another. This in turn is easy to demonstrate to those who agree that bodies are composed of parts. Compare the deductions I have made from my assumption [suppositions]—about vision, salt, winds, clouds, snow, thunder, the rainbow, and so on—with what the others have derived from their assumptions on the same topics. I hope this will be enough to convince anyone unbiased that the effects which I explain have no other causes than the ones from which I have deduced them. None the less, I intend to give a demonstration of it in another place. (Descartes to Morin, 13 July 1638, AT II 200; CSMK 107)

In comparing the results he has achieved in his physics with the results of traditional philosophies, Descartes rejects the Scholastic system of knowledge once more and claims the efficacy of his method grounded in the mind. By means of suppositions and experimentation and deducing from these suppositions, Descartes has been able to explain several phenomena—vision, salt, winds, clouds, and rainbow. Still, in the Discours and Essais, Descartes writes in a hypothetical way: Since he does not provide the principles of his philosophy, suppositions represent the point of departure for deduction, and knowledge follows an a posteriori path. A plain description of such principles is provided only several years later in his school text, Principia philosophiae.90

2.3.3

A History of Natural Particulars in the Principia

The Principia ultimately provides the principles of Descartes’s philosophy from which he would be able to achieve the knowledge of all natural particulars—this is his entire physics. In article 64 of Part 2, Descartes claims that “these principles explain all natural phenomena, and enable us to provide quite certain demonstrations regarding them” (Principia philosophiae, II, art. 64, AT VIII-1 78; CSM I 247).91 From the definition of extended matter (and the modes of extension), one may deduce the knowledge of particular bodies, according to Descartes, because these

89

Cf. Sgarbi 2023: 123. Morin reacted to Principia as well in his Astrologia gallica (1661), cf. Garber 1996b. 91 Cf. de Buzon 1996. Gaukroger 1989: 103–104. 90

2.3

Observations in a System: Knowledge of Particular Bodies from. . .

47

principles allow to “explain all natural phenomena” (Principia philosophiae, II, art. 64, AT VIII-1 79; CSM I 247). In Part 3 of the Principia, this certainty is, however, broken. Let us explore this aspect. When identifying phenomena with experimental knowledge [De phaenomenis, sive experimentis], in article 4 of Part 3, Descartes describes the usefulness of experimentation within his philosophical program. As seen earlier, experimentation becomes necessary to counteract the vastness of nature and the fecundity of the principles, as well as the impossibility of enumerating all effects within the mind. The problem of defining the right combination of cause and effect persists. In this case, experimentation works putting forward a short history of the natural phenomenon [brevem historiam praecipuorum naturae phaenomenωn], operating as an instrument to “direct the mind to a consideration of some effects rather than others” (Principia philosophiae, III, art. 4, AT VIII-1 81; CSM I 249). What results is a more exhaustive knowledge of particular bodies. Something more surfaces in the middle of Part 3. Although Descartes affirms that deduction is always correct, he raises some doubts regarding its point of departure, namely his suppositions. In article 44, Descartes suggests that his suppositions are mere hypotheses, “which [are] perhaps far from the truth” (Principia philosophiae, III, art. 44, AT VIII-1 99, and AT IX-2123; CSM I 255). Even in this case, knowledge may be sufficiently worthwhile if anything “deduced from it harmonizes with [. . .] observations [. . .] {because we shall be able to use it just as effectively to manipulate natural causes so as to produce the effects we desire}” (Principia philosophiae, III, art. 44, AT VIII-1 99, and AT IX-2123; CSM I 255). Despite his promises of providing a deductive chain from the principles to the effects, Descartes here opts for a hypothetical argument, and experimentation plays a fundamental role. Accordingly, “[one] cannot determine by reason alone” the effects of these hypotheses (or assumptions,) and “experience alone must teach us which configurations” these bodies take. As previously seen, experimentation provides knowledge with data or the particular object. In this sense, “we are thus free to make any assumption on these matters with the sole proviso that all the consequences of our assumption must agree with our experience” (Principia philosophiae, III, art. 44, AT VIII1100–101; CSM I 256–257). At this point, Descartes seems to claim that, more than the knowledge of principles, that is, deductive knowledge, the only way to acquire science is to perform experimentation.92 In knowing particular bodies, the appeal to experimentation is more than a mere necessity of gathering varieties, because experimentation helps provide certainty in hypotheses and suppositions, which at this stage appear as the only serious point of departure for scientific knowledge. From the rationalistic epistemology of the Regulae, in the Principia, Descartes appeals to the importance of hypotheses and experimentation to attain scientific knowledge. Still, this is not a mere contrast between two epistemologies, namely on the one hand, the knowledge a priori (from causes to effects) and, on the other hand, the

92

Cf. Garber 1978: 145.

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knowledge a posteriori (which now becomes hypotheses controlled by experimentation).93 A combination of deduction and experimentation persists in Descartes. The knowledge derived from experiments (the one we use to define effects) does not develop outside the system of knowledge grounded in the mind—i.e., a priori. The hypothetical argument, which may be a better way of coming to grips with the world and particular bodies, remains framed within the rational system set forth by his method.94 As a result, Descartes’s use of experiments, observations, enumerations, collections, and natural history, as well as daily experience—the quotidiana experientia— is regulated by the certainty of the mind,95 whose principles are provided, and whose certainty is established in Part 1 of the Principia. As a consequence, the knowledge of particular bodies lies within a system of knowledge grounded on the mind.96 This is confirmed by Descartes himself at the end of the text. Here, he affirms that “no phenomenon of nature [. . .] has been overlooked in this treatise” (Principia philosophiae, IV, art. 199, AT VIII-1323; CSM I 285), suggesting that his principles have enabled him to explain the visible world in its entirety by means of a combination of experimentation and deduction. In article 200, he claims to have “explain [ed] the general nature of material things [by means of] principles [. . .]. [And] considered the shapes, motions and sizes of bodies, and examined the necessary results of their mutual interaction in accordance with the laws of mechanics, which are confirmed by reliable everyday experience” (Principia philosophiae, IV, art. 200, AT VIII-1323; CSM I 286). From his principles, and following the laws of mechanics, Descartes has thus deduced the nature of diverse bodies, producing an entire physics. Given this, in article 203, he summarizes his practice in knowing the nature of particular bodies from the principles. First, I considered in general all the clear and distinct notions which our understanding can contain with regard to material things. And I found no others except the notions we have of shapes, sizes and motions, and the rules in accordance with which these three things can be modified by each other—rules which are the principles of geometry and mechanics. And [. . .] all knowledge [. . .] of the natural world must necessarily be derived from these notions; for all the other notions we have of things that can be perceived by the senses are confused and obscure [. . .]. Next, I took the simplest and best known principles, knowledge of which is naturally implanted in our minds; and working from these I considered [. . .] firstly, what are the principal differences which can exist between the sizes, shapes and positions of bodies [. . .] and secondly, what observable effects would result from their various interactions. Later on, [. . .] I observed just such effects in objects . . . (Principia philosophiae, IV, art. 203, AT VIII-1 326, AT IX-2 321; CSM I 288).97

93

Cf. Lojacono 1996b, 427-ss. In this sense, I disagree with Daniel Garber’s conclusion on certainty in the Principia, see Garber 1996a: 363. 95 Principia philosophiae, II, art. 38, AT VIII-1 63; CSM I 241. Cf. Brown and Normore 2020. 96 Where this is possible: As we know, Descartes claimed he did not add the sections on animals and plants, and human beings, because of some uncertainty and the lack of experiments. 97 My interpretation of this passage differs from Garber’s, cf. Garber 1996a: 357. 94

2.4

Conclusion

49

Putting all these passages together, the system of knowledge in Descartes’s philosophy appears clear. Accordingly, knowledge begins with clear and distinct notions, which lie naturally within the mind. These notions are the principles of his philosophy. Then, from these simple notions, which in physics consist in the mechanical reduction of bodies to particles with different shapes, sizes, and motions, one could deduce the knowledge of bodies in general. The interactions of these modes result in the diverse effects one would observe, and the laws of mechanics and geometry regulate these interactions. Finally, one visualizes these interactions in bodies by means of experimentation, going back from the effects to the causes—he “consider [s] the observable effects and parts of natural bodies and track[s] down the imperceptible causes which produce them” (Principia philosophiae, IV, art. 203, AT VIII1326; CSM I 289).98 The explanation of all the phenomena of nature and “the properties relating to magnetism, fire and the fabric of the entire world” are ultimately “deduced from just a few principles” (Principia philosophiae, IV, art. 205, AT VIII-1328; CSM I 290).

2.4

Conclusion

From the Regulae ad directionem ingenii, Descartes shapes a new system of knowledge, whose certainty belongs to the cognitive productivity of reason, especially from two intellectual activities, intuition, and deduction. In rejecting knowledge based on opinions, history, and syllogism, Descartes establishes a new epistemology. However, his epistemology changed through the years, as he faced the attempts to know particular bodies and opened up to not only experimentation, observations, natural history but also hypotheses and conjectures. As I have highlighted, this is not a complete change in his philosophy, because experimentation was not excluded from the early epistemology of the Regulae, in which the method regulates experimentation by means of a few procedures—arrangement in series, comparisons, enumeration, and induction. Nonetheless, the appeal to experimentation appears more and more important insofar as he started dealing with particular bodies because reducing the variety of nature to ideas or mathematical proportion appears rather complex. In the early 1630s correspondence, the appeal to experimentation acquires a more prominent condition, as a priori knowledge (from the principles or causes to the effects) is insufficient, and perhaps ineffective as one aims to deal with individuals and more complex bodies. Observations (lists of qualities, natural history, and so on) are thus a more fundamental tool to provide knowledge with data and help deduction. The Discours seems to acknowledge this issue and extends it a bit, as in Rule 3 of the method Descartes suggests to start the chain of deductions from a supposition or

98

See art. 204, AT VIII-1327, AT IX-2322; CSM I 289.

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hypothesis, which he clearly did in medicine, optics, and meteors—namely in the Essais. Hypotheses and suppositions play a major role even in the Principia, despite the metaphysical foundation of Part 1. Despite providing the principles of his philosophy, Descartes felt compelled to begin the investigation of natural bodies with a history of natural phenomena, hypotheses, and conjectures as crucial aids to achieve his natural philosophical program. In sum, an epistemological path surfaces: From the extreme rationalism of his early works, Descartes later opened to experimentation and observations, especially driven by the importance to deal with particular bodies. In the following chapters, I explore how far he achieved his natural philosophical program, investigating Descartes’s work in diverse fields of science, from a definition of nature to chymistry (or mineralogy) botany, and zoology.

Chapter 3

Nature

Abstract In this chapter, I focus on Descartes’s physics. According to it, nature is extended matter, a uniform solid body made of moving and arranging corpuscles with some size and shape. Nature is a geometrical space. In Descartes’s early physics, Le Monde, he invented nature as a mathematical equation, and bodies take different figures following the mechanical laws of nature (i.e., the laws of motion). Yet, in both Les Météores and the Principia, external, actually existing bodies play a more central role, and Descartes’s physics starts from the observation of these bodies and the aggregate of corpuscles. In this chapter, I analyze these various interpretations and reconstruct Descartes’s attempts to bridge the gap between the geometrical definition of nature and the actually existing world. Finally, I also examine Descartes’s uses of observation, which in Le Monde serves to confirm his theory while in the later texts appears as the point of departure to know the universe. In the Discours, Descartes claimed it was possible to become “lords and masters of nature,” as the method described in the text allows for the knowledge of “the power and action of fire, water, air, the stars, the heavens and all the other bodies in our environment” (Discours de la Méthode, VI, AT VI 62; CSM I 142–143). This discipline is physics, and it explains all phenomena of nature, broadly intended, from cosmology to natural philosophy.1 Accordingly, from the knowledge of nature (and the knowledge of natural particulars), one would be able to infer several rules of medicine in order to treat all diseases, infirmity of old age, and extend life.2 In this sense, there is no breach in Descartes’s philosophy, which has the shape of a chain of knowledge. In the Lettre-Préface to the French translation of the Principia, Descartes claimed that all sciences develop from physics, as branches from the trunk of a plant. Defining nature is therefore a necessary point of departure in Descartes’s

1

Descartes to Mersenne, November 13, 1629, AT I 69. Discours de la Méthode, VI, AT VI 62–63; CSM I 143. Cf. Descartes to Newcastle, October 1645, AT IV 329. 2

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 F. Baldassarri, René Descartes’s Natural Philosophy and Particular Bodies, Studies in History and Philosophy of Science 60, https://doi.org/10.1007/978-3-031-48663-0_3

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chymical and biological investigations, as all knowledge is related to physics—and takes life from its metaphysical roots. Yet, the definition of nature is not without questions and challenges. In his physics, Descartes did not content himself with knowing the world, but constructed, or invented a new one by means of a few rational operations. Still, moving from the mind to reality, that is, from the rationally constructed world to the actual one, uncovers problems he needed to deal with in his philosophical program. A first issue concerns the roots of Descartes’s physics, namely its metaphysics (on this, see again the example of the tree). Daniel Garber has detailed the connection between metaphysics and physics with great care and attention, as Descartes’s mechanist system of metaphysics and natural philosophy produced a specific understanding of nature and its laws.3 Accordingly, the roots of the Cartesian definition of nature and natural bodies are in Meditationes de prima philosophia (1641), in which Descartes provided the formulation of a distinct concept of corporeal nature. In Meditatio 5 and Meditatio 6, he discussed the essence of material things. Yet, Descartes also claimed that “nature [in general] is God himself, or the coordination established on the ordered system of created things by God” (Meditationes de prima philosophia, VI, AT VII 80; CSM II 56 [translation modified]). At this stage, the equivalence between nature and God is complete. In Descartes et la fabrique du monde, Édouard Mehl has significantly investigated this topic, including a reconstruction of Descartes’s context and the debates with his contemporaries.4 It is important to note that nature appears as a coordination, or a systematization of bodies, originally created by God, according to Descartes. I am not elaborating this issue, as I aim to focus less attention on the metaphysical ground of Descartes’s philosophy of nature. In this chapter, I discuss his attempts to study nature as an ordered system of bodies. Significant changes and transformations characterize Descartes’s studies of nature, as the structure of the early physics of Le Monde differs from the physics of the Principia—these changes parallel some of the changes in Descartes’s method discussed in Chap. 2.5 The first text reveals an original reduction of nature to mathematics, while the latter necessarily grounds the veracity of physics in God. Differences lie not only in metaphysics or in the rational construction of nature but also in the structure of physics itself, as Descartes moved from a mathematical representation of nature to the recognition of the approximations and shortcomings of this project, as he discusses particular bodies from a corpuscularian perspective. I am going to discuss the originality of Le Monde in the first section of this chapter, as I explore Descartes’s invention of nature by means of imagination. In the second section, I investigate Descartes’s laws of nature and their application to the knowledge of particular bodies. Applying his matter theory and the mechanization of

3

Cf. Garber 1992: esp. chap. 3, 63–93. For a more complex reconstruction, see Machamer et al. 2005. 4 Cf. Mehl 2019a: esp. chap. 2, 61–126. See also, Ariew 2011. More recently, see Guidi 2021b. 5 Cf. Schuster and Brody 2013.

3.1

A Theoretical Model: The World Imagined

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nature to particular bodies marked Descartes’s attempt to bring his investigation of nature to completion. This is a trait d’union between his early and later physics. Yet, a difference surfaces: While in Le Monde the veracity of the mechanization of particular bodies lies within the mind, and is proved a priori by means of mathematical truths, in the Principia, he grounds physics on the metaphysical principles and the existence of the world, through which he aims to fill the gap between his mechanization and the nature of particular phenomena. This attempt ultimately surfaces in his uses of observation, the topic of the final section of this chapter. Accordingly, observation arises as a necessary tool to confirm the validity of his rational definition of nature. An outstanding combination of his definition of nature by means of imagination, his theory of extended matter, and the principles of physics, on the one hand, with the observation of nature, on the other hand, specifies Descartes’s natural philosophy. This will ultimately pave the way for the study of particular bodies.

3.1

A Theoretical Model: The World Imagined

In Le Monde, after having claimed that (1) the physical world differs from our perceptual images, and that (2) a few macroscopic phenomena may be accounted for in micro-corpuscularian terms, Descartes constructs the hypothesis of a new world. In Chapter 6, he moves from a supposition, consisting of making thought wander beyond this world and devise a new world in “imaginary spaces” (Le Monde VI, AT XI 31; G 21).6 In this creation, God fills such spaces with extended matter, as our imagination could not see any void in it. This is the fable of the world.7 From a methodological perspective, physics starts neither with a historical reconstruction of someone else’s interpretation nor with sensory experience. The starting point is an exercise of the imagination, that is, an exercise of reason,8 and not a mere fiction.9 A theoretical design of the world arises, combining hypothesis and imagination.10 This is confirmed a bit later, as by imagining the matter “as we fancy,” Descartes assumes that:

6

See Verbeek 2000. Stabile 2008. Cf. Sepper 1996: 211–238. Cf. Le Monde, V, AT XI 31; G 21. Descartes to Mersenne, November 25, 1630, AT I 179. One should note that, contrarily to the fables or histories described in Part 1 of the Discours, this fable is not chosen to conceal the truth but to make it better understood. Cf. Cavaillé 1991. 8 On the connection between imagination and reason, see Sepper 2013: 286-ss. and the Introduction of this book. On imagination and extension, see Anfray 2020. 9 Gilby 2019. 10 Cf. Discours de la Méthode, V, AT VI 42; CSM I 132: “I therefore supposed that God now created, somewhere in imaginary spaces, enough matter to compose such a world; that he variously and randomly agitated the different parts of this matter so as to form a chaos as confused [. . .] he then did nothing but lend his regular concurrence to nature, leaving it to act according to the laws he established.” 7

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it does not have the form of earth, fire, or air, or any other more specific form, like that of wood, stone, or metal, nor does it have the qualities of being hot or cold, dry or moist, light or heavy, or of having any taste, odour, sound, colour, light, or of any other quality in nature of which there might be said to be something which is not known clearly by everyone. (Le Monde, VI, AT XI 33; G 22)

In rejecting substantial forms and qualities, as well as natural elements, which are not evidently known, Descartes claimed that the matter composing the new world is purely rational. Additionally, this matter is not the “prime matter of the Philosophers, which they have stripped so thoroughly of all its forms and qualities that nothing remains in it which can be clearly understood” (Le Monde, VI, AT XI 33; G 22). In contrast, Descartes conceives of the world “as a real, perfectly solid body, [as its matter] uniformly fills the entire length, breadth, and depth of this great space in the midst of which we have brought our mind” (Le Monde, VI, AT XI 33; G 22).11 Matter is therefore an actual solid body, uniformly extended. While traditional and scholastic philosophers have interpreted nature as a combination of qualities, substantial forms, elements, and matters and have even included a prime matter that is a substratum underlying forms and qualities, Descartes rejected all these notions as they fail to account for nature.12 Indeed, these features correspond to an obscure and unintelligible interpretation of the world. Challenging scholastic philosophy, Descartes imagines or conceives of a new world composed of matter as a real solid body. In principle, this world is indistinguishable from the actual world. Such an ontological identification of natural and artificial objects constitutes the core of his mechanical physics, as Helen Hattab has recently shown.13 Two issues surface. First, the language of this fable is that of reason, and not the fable described in the Discours; so he forms this piece of matter in the reason. This entails that this piece of matter is known in a clear and distinct way. A strong consequence of this claim is that nature lies within the mind, thus availing a metaphysical reconstruction of physics. A less strong reading would concede that the imagination of such a new world is an intellectual conception, whose knowledge is clear and evident. This is consistent with the epistemology of the Regulae. Later in the text, Descartes claims that the supposition of extended matter is perfectly known, and no one could pretend to ignore it. First, this supposition is consistent with everyone’s imagination of matter. In this sense, this knowledge resides within our reason—in the epistemological language of the Regulae, one would say this supposition is a simple nature or a seed of truth within the mind. Second, imagining nature as extended matter is the ground of every imagination of other bodies, and this is necessarily known. In this sense, Descartes claims that “there is nothing simpler or more easily grasped in inanimate creatures” (Le Monde, This definition fits with the res extensa. For the Scholastic view of nature, and specifically in Suarez, see Hattab 2009: 55–56. On Descartes’s reply to Scholastic substantial forms, see Hattab 2009: 85–154, and 186–220. 13 Hattab 2019: 137. See also Hattab 2009: 126–135. I will return to this point in Chap. 4, while dealing with Descartes’s discussion of salt. 11 12

3.1

A Theoretical Model: The World Imagined

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VI, AT XI 34; G 23) than the fact that extended matter composed them. This definition of the world as extended matter is the point of departure for any knowledge of bodies in particular. The second issue is that the only attribute of matter is the extension in length, breadth, and depth. This is Descartes’s theory of matter. In focusing on the qualities of extended matter, Descartes adds that “matter may be divided into as many parts and shapes as we can imagine, and that each of its parts can take on as many motions as we can conceive” (Le Monde, VI, AT XI 34; G 23). Ruled by reason, three definitions of matter surface. The first is that matter is in(de)finitely divisible. The second is that these parts may take different shapes. The modes of extension thus regulate matter, and its pieces could take all shapes and figures. The third is that motion is a characteristic or mode of matter. This is a crucial point. Accordingly, all particularities of nature could be reduced to matter and motion, and nature itself is not just an essence, but a principle of operation. In nature, motion is what shapes matter and makes it acquire different figures. According to Descartes, the differences between parts consist “wholly in the diversity of motions [God] gives to its parts,” for God, who “from the first instant of their creation [. . .] causes some [parts] to start moving in one direction and others in another [. . .], causes them to continue moving thereafter in accordance with the ordinary laws of nature” (Le Monde, VI, AT XI 34; G 23). Laws of nature significantly enter the picture of physics. While nature might be a disordered and muddled chaos of matter—Descartes supposes the worst possible case, namely that God might have created nature in an extremely chaotic way—the laws of nature provide order and proportion to such a chaos. Accordingly, these laws “are sufficient to cause the parts of this chaos to disentangle [. . .] and arrange [. . .] in such a good order,” resulting in “a world in which one will be able to see not only light, but all the other things as well, both general and particular” (Le Monde, VI, AT XI 34–35; G 23). The laws of nature allow one to recognize an order in the chaos, setting the path of knowledge. The knowledge of this order is the goal of Cartesian physics. Before entering into this point, let us summarize Chapter 6 of Le Monde. In this chapter, Descartes has set up an intelligible, theoretical model, conceived as a hypothesis, by imagining a new world as a piece of matter. In this sense, imaginability is the main requirement to acquire physical knowledge.14 The grounding intuition is that nature is made of extended matter, which entirely fills the space. In the lexicon of traditional philosophy, Descartes here claims that extension, “or the property it has of occupying space, [is] not an accident, but its true form and essence” (Le Monde, VI, AT XI 36; G 24). Descartes thus strips nature of any qualities but extension, which is the only attribute of matter. As a mode of extension, motion regulates the variations in

Le Monde, VI, AT XI 36; G 24: “Since everything I propose here can be imagined distinctly, it is certain that even if there were nothing of this sort in the old world, God can nevertheless create it in a new one; for it is certain that He can create everything we imagine.” 14

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matter, whose parts are infinitely divisible and able to take all shapes, therefore producing different bodies. The theory of extended matter is the theoretical framework grounding physics, the point of departure of science. A science of nature does not follow from the fact God has created it in a certain way as God’s ways are unintelligible, according to Descartes. What is intelligible is the knowledge of extended matter, which lies within reason. Indeed, “things [are disposed] in number, weight, and measure,” a knowledge “so natural to our souls that we cannot but judge them infallible when we conceive them distinctly” (Le Monde, VI, AT XI 47; G 31).15 From this, one should find order and proportion in the arrangement of extended matter to acquire scientific knowledge.16 This is possible by knowing the laws of nature, the topic of Chapter 7 of Le Monde. At the beginning of this chapter, Descartes provides a short definition of “Nature [. . .] not [as] some deity or other sort of imaginary power. Rather, [nature] signifies matter itself” (Le Monde, VII, AT XI 37; G 25). Then, he focuses on some metaphysical considerations. Accordingly: God continues to preserve [nature] in the same way that He created it. For it necessarily follows, from the mere fact that He continues thus to preserve it, that there must be many changes in its parts which cannot, it seems to me, properly be attributed to the action of God (because that action never changes) and which I therefore attribute to Nature. The rules by which these changes take place I call the “laws of Nature.” (Le Monde, VII, AT XI 37; G 25)

This passage contains a crucial argument, as Descartes claims that the changes in nature do not pertain to the action of God, but to nature itself, and specifically to the laws of nature. Changes are therefore internal to his theory of matter. He explains this separation as he adds that “from the time [parts of matter] begin to move, they also begin to change and diversify their motions,” and God, who “created them, [. . .] does not preserve them in the same state.” The differences between bodies, thus “occur, as if by accident” (Le Monde, VII, AT XI 37–38; G 25). A few important issues surface. The first is the action of God and his relationship with nature. Theo Verbeek has brilliantly claimed that Descartes’s differentiation between God’s immutability and the continuous changes in nature has a scientific significance.17 Accordingly, God creates the conditions for the laws of nature, and is the assumption of their validity, but changes are within nature itself. Descartes thus fleshes out that, while God created straight motions, the “various dispositions of matter [. . .] render the motions irregular and curved” (Le Monde, VII, AT XI 46; G 30). Not only changes and motions are within nature, but nature (namely extended matter) is what makes motions differ and produce different bodies. Nature is thus the source of changes in bodies, through the motions of particles. Yet, Descartes claims that these motions can be known, as they are similar to “the lines of the geometers—[as] motion makes bodies pass from one place to another 15

He also called this an eternal truth. Cf. Descartes to Mersenne, May 6, 1630, AT I 149–150. The echo of Rule 5 is noticeable. Cf. Regulae ad directionem ingenii, V, AT X 379. 17 Verbeek 2000: 152. 16

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and successively occupy all the spaces which exist in between” (Le Monde, VII, AT XI 41; G 27). In this sense, one could know nature by means of mathematics—as Descartes reduces bodies to their aggregate of matter due to motion, which can be geometrically known. The consequence is striking. The world is “an arithmetic machine” (Stabile 2008: 344)18 and “physics is nothing but geometry—a sort of geometry where the problems have to do with the explanation of natural phenomena” (Descartes to Mersenne, July 27, 1638, AT II 268; CSMK 119)19 as Descartes claims. What results is clear. In stripping nature of the qualities and diverse forms that populated the cosmos of Aristotelian tradition and the nature of Renaissance philosophers,20 Descartes has invented nature as a theoretical model by means of an act of reason. As he writes in the Discours, “there is absolutely nothing [. . .] clearer and more intelligible” than matter, “with the exception of [. . .] God and the soul” (Discours de la Méthode, V, AT VI 42; CSM I 132). The imaginary space in which Descartes conceives of the new world is the geometrical space, and the rules of nature have the form of an equation describing fundamental quantifiable physical notions, through which one knows the various compositions of bodies. Mathematics is what provides order and proportions to the chaos, and it is the way to know nature.21 In sum, the invention of nature belongs to reason, and although “our senses [. . .] experience [. . .] seemed manifestly contrary to what is contained in these rules, the reasoning that has taught me them seems strong” (Le Monde, VII, AT XI 43; G 28). Within this account, in Chapters 8 to 12, Descartes sets out his heliocentric cosmology, taking the shape of an evolutionary history of cosmology.22 The universe thus consists of an indefinite number of contiguous vortices, the theory of planetary orbits, within which celestial bodies compose and move. The text, however, ends with Chapter 15 on the Earth, without dealing with particular bodies.

3.2 3.2.1

Constructing Nature: A Mechanical World Rules of Nature and Elements in Le Monde

The rules of nature operate by providing matter with an intelligible order and reveal the motions that make matter arrange and compose bodies. In the Discours, Descartes claims that “in consequence of these laws, the greater part of the matter of this

18

Cf. Colloquium with Burman, AT V 160. Gaukroger 1989: 108. Cf. Descartes to Mersenne, March 11, 1640, AT III 39; CSMK 145. 20 On nature in the sixteenth and seventeenth centuries, see Lenoble 1968. Erhard 1981. Hadot 2004. 21 On mathematicians, see Le Monde, VII, AT XI 47; G 31. 22 Cf. Gaukroger 2002: 15-ss. 19

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chaos had to become disposed and arranged in a certain way, which made it resemble our heavens; [. . .] an Earth, some planets and comets [. . .] a Sun and fixed stars.” Yet, he adds to have explained “how mountains, seas, springs and rivers could be formed naturally [. . .], and how metals could appear in mines, plants grow in fields, and generally how all the bodies we call ‘mixed’ or ‘composite’ could come into being” (Discours de la Méthode, V, AT VI 44; CSM I 133). Consistently with his choice not to reveal his principles, Descartes does not expound the laws of nature in the Discours but just refers to them as a feature of his earlier physics. In Le Monde, he devises three laws of nature. The first is that “matter always continues in the same state unless collision with others forces it to change its state” (Le Monde, VII, AT XI 38; G 25). The second is that “when one of these bodies pushes another it cannot give the other any motion except by losing as much of its own motion at the same time” (Le Monde, VII, AT XI 41; G 27). These two laws describe the conservation of motion, while the third law deals with the direction of motion. The latter asserts that “when a body is moving, even if its motion most often takes place along a curved line [. . .] nevertheless each of its parts individually tends always to continue moving along a straight line” (Le Monde, VII, AT XI 43–44; G 29). Accordingly, the tendency or inclination of a moving body is always rectilinear. From the principle of extended matter and from these three laws of nature, Descartes then deduces several effects. He describes the formation of all celestial bodies by means of the mechanical movement of matter. Cosmology consists of an interaction between three kinds of particles, described and isolated earlier in the text, in Chapter 5 of Le Monde. These corpuscles differ solely in size, arrangement, and motions that are their accidental modes. The “first, which may be called the element of fire [is] the most subtle and penetrating fluid in the world [. . .]. I imagine its parts to be smaller and to move much more quickly than any of the parts of other bodies” (Le Monde, V, AT XI 24; G 17). Instead of imagining “the ‘form’ of fire, the ‘quantity’ of heat, and the ‘action’ of burning to be very different things in the wood” (Le Monde, II, AT XI 7; G 6), Descartes claims that fire consists of the motions of these small corpuscles within a body. And its knowledge consists of understanding these motions. Since the parts of the flame “have the power to consume the wood and to burn it” by their motions, “it is enough to conceive of their motions [. . .]. [. . .] and the flame will need possess no other quality, and we shall be able to say that it is this motion alone that is called now ‘heat’ and now ‘light,’ according to the different effects it produces” (Le Monde, II, AT XI 9: G 8). By claiming there is no internal faculty to burn, and no quality, Descartes states that to know the burning process, one should postulate the motion of small corpuscles, which produces various effects. One could thus reduce these variations to a geometrical model. The second element is “the element of air, [. . .] a very subtle fluid in comparison with the third.” These corpuscles have “some size and shape [. . .] [and are] round and joined together like grains of sand or dust.” Yet, around them, many small gaps remain, as “the first element [. . .] slides into these” (Le Monde, V, AT XI 25; G 17). This element consists of a fluid set of corpuscles, composing bodies of a middling condition. The third element is that of earth. Its corpuscles are larger and more solid,

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and move slowly, ultimately being closely joined together as they have the force to resist the motions of other bodies. These types of matter have different optical properties: The first element is luminous, the second transparent, and the third opaque; these qualities are related to their mobile capacity. The properties of these three elements consist of their “motion, size, shape, and arrangement” (Monde, V, AT XI 26; G 18).23 By mixing and operating one upon another, these elements construct all bodies, or corrupt them, as it occurs with fire burning woods or metals.24 The result is twofold. First, he rejects the qualities of the Schoolmen, as heat, cold, moistness, and dryness fail to explain nature and need an explanation themselves. And he also rejects Scholastic forms or natural complexion, natural places, and natural purity, as bodies could be ultimately reduced to extended matter, that is, to these three elements.25 Second, in reducing natural varieties to a combination of corpuscles, Descartes focuses on the mechanical, internal, and structural order of matter. In this sense, although celestial bodies may differ—the Sun and the stars are composed with the first element; the skies with the second; and the Earth, planets, and comets with the third—the same extended matter and the same rules of nature compose all of them. As Descartes fleshes out, the same movement could thus make the particles of fire liquefy and burn something, but produce a different effect in the particles of air, for one should take into account the size of particles as well as of motions.26 In this sense, the only difference between bodies consists of the size and speed of the corpuscles composing the bodies. These mechanical features explain all different activities and diverse bodies, according to Descartes, resulting in a mechanical physics.27 In moving from the cosmological bodies to the Earth, Descartes then claims that the parts of the three elements compose the bodies around us, although they should be generally ascribed to the third element, “because of their size or the difficulty they have in moving.” Similarly to the case of “sponges [. . .] with many pores which are always full of air or water [though] we do not think that these fluids enter into its composition” (Le Monde, V, AT XI 30–31; G 21), the same applies for bodies on the Earth, as the first and second elements fill the pores of the third element, but we do not think that these fluids enter into their composition. Yet, a physical account of the various bodies ultimately consists of investigating the mechanical combination between the motion and size of corpuscles, and these three elements. This is something he claims in a letter to Villebressieu in 1631, where he writes that “there is only one material substance that receives from an external agent the action or the mode for local movement, from which different figures and modes

23

Cf. Lynes 1982. On the force of fire in melting metals, Le Monde, III, AT XI 14–15; G 11. I investigate this issue in Chap. 4 in more detail. 25 Cf. Monde, VII, AT XI 25–26, 28–29. 26 Monde, III, AT XI 15; G 12. 27 On Descartes’s mechanical physics, see Gabbey 1993. Garber 2000. Garber and Roux 2013. See also Hattab 2019. 24

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derive transforming matter into what we see” (Descartes to Villebressieu, Summer 1631, AT I 216). Nevertheless, this investigation is not in the pages of Le Monde.

3.2.2

The Mechanization of Material Objects: The Principia, Part 2

A mechanistic account of nature also composes Part 2 of his Principia philosophiae, in which Descartes provides the principles of physics and the principles of material objects.28 In this part, Descartes moves from the definition of the existence of material objects to the account of the laws of nature, and he grounds the real existence of the world of bodies in the principles of metaphysics of Part 1—which goes back to Meditatio 3.29 However, it is sensory perception that makes us aware of “some kind of matter, which is extended in length, breadth and depth, and has various differently shaped and variously moving parts which give rise to our various sensations of colours, smells, pain and so on” (Principia philosophiae, II, art. 1, AT VIII-1 40; CSM I 223). This text presents an unexpected claim. While Descartes states that extension is the main attribute of matter, consistently with Le Monde, a difference with his early text immediately surfaces. Here, he claims that the idea of the res extensa “possessing all the properties which we clearly perceive to belong to an extended thing” comes “from things located outside ourselves” (Principia philosophiae, II, art. 1, AT VIII-1 41; CSM I 223).30 While in Le Monde the knowledge of material bodies entirely lies in the mind, as the device of the imaginary world uncovers, and, in this sense, a strict interpretation of Le Monde implies the conceptual independence of physics, in the Principia Descartes follows a more traditional route, and the external body is experienced through sensation and its existence is proved by the metaphysical argument that God is not a deceiver. In the Principia, body and mind are metaphysically different [a mente nostra diversa est]. As a result, while in Le Monde nature is a construction of the mind, and nature lies within the mind, in the Principia, nature (i.e., the existence of an external set of bodies) is given, and the mind may know it by applying the laws of nature. Yet, a union between the mind and the body should be provided.31 This entails a consequence in the structure of physics in both the Principia and Le Monde. While in his earlier text he moves from the imagined world, which he conceives as true (given the fact that it lies within the mind) and then uncovers an accord between the world imagined and the actual, existing one, in the Principia, he applies the rules of nature to bodies and matter that are actually existing. In other

28

See the detailed reconstruction in de Buzon and Carraud 1994. See Principia philosophiae, II, art. 1, AT VIII-1 40–41; CSM I 223. 30 Cf. Carraud 1996. 31 It looks possible that two slightly diverse metaphysics buttress Descartes’s early and later physics, but I am not dealing with this aspect. 29

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words, while in Le Monde the consistency between physics and nature lies within the mind, in the Principia, the laws of physics bridge the gap in the metaphysical distance between mind and body, providing a union between bodies and the idea one has of them. Since the applicability of the laws of nature to natural bodies follows directly from his derivation of the laws from divine immutability, this entails that the bridge between the mind and nature has a metaphysical ground.32 Let us now examine Descartes’s physics as it surfaces in Part 2 of the Principia. From articles 1 to 22 of Part 2, Descartes presents his theory of matter, while from articles 23 to 63, he presents his theory of motion. In article 64, he summarizes his mathesis, as I discussed in Chap. 2. The first 22 articles thus contain Descartes’s definition of nature, as “something extended in length, breadth and depth” (Principia philosophiae, II, art. 4, AT VIII-1 42; CSM I 224) and stripped of any perceivable qualities (namely secondary qualities such as hardness, weight, or color). Within his matter theory, the body consists of extension alone. Corollaries of his theory of matter are (1) the rejection of void, (2) the impossibility of atoms (as bodies are indefinitely divisible), and (3) the indefinite extension of the universe. A corporeal substance is therefore its quantity of extended matter—as he writes in articles 8 to 12—and existing in space. In articles 13 and 14, Descartes rejects the Aristotelian doctrine of places. In identifying place and space with the body, Descartes therefore explains rarefaction as a replacement of matter, as the “quantity of matter does not depend on their heaviness or hardness, but solely on their extension, which is always the same for a given vessel” (Principia philosophiae, II, art. 19, AT VIII-1 51; CSM I 231) whether it is filled with lead or gold or any other body. This uncovers another issue, namely the problem of the identification and individuation of bodies in Descartes. In article 11, he claims that if “we leave out everything we know to be non-essential to the nature of [a stone],” therefore excluding its hardness, color, heaviness, cold, heat and other qualities, “nothing remains in the idea of the stone except that is something extended in length, breadth and depth” (Principia philosophiae, II, art. 11, AT VIII-1 46; CSM I 227).33 As a result, nothing specifies the nature of the stone, but its extension in matter, which is the attribute of bodies. This is the ground of physical knowledge. In article 22, then, Descartes rejects the doctrine of a radical difference between sublunary and celestial bodies.34 In being nothing but extended matter, all bodies are ontologically reducible to a mechanical model, and nature is a homogeneous piece of matter. No variations surface, as the only difference in degree pertains to extension, and not to other qualities.35 In the next articles, Descartes undertakes the attempt to deduce diverse bodies from homogeneous and undifferentiated extended matter.36 This is a significant

32

See Principia philosophiae, II, art. 36, AT VIII-1 61–62; CSM I 240. See the case of wax in the Meditationes de prima philosophia. 34 Principia philosophiae, II, art. 22, AT VIII-1 52; CSM I 232. 35 Cf. de Buzon and Carraud 1994: 69. 36 Rodis-Lewis 1950. Cf. Laporte 1950: 186–189. 33

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passage in the Principia, as it moves from the identity of extension to the ways bodies differentiate. In article 23, he writes that “the matter existing in the entire universe is thus one and the same, and it is always recognized as matter simply in virtue of its being extended. All the properties [. . .] are reducible to its divisibility and consequent mobility in respect of its parts” (Principia philosophiae, II, art. 23, AT VIII-1 52; CSM I 232). As in Le Monde, motion produces bodily variation. This is a real distinction, as one perceives these properties and these bodies. In article 25, he defines a particular body as “whatever is transferred [together]” (Principia philosophiae, II, art. 25, AT VIII-1 53–54; CSM I 233).37 The unity of movement is what makes a singular, individual body. Indeed, individuality is contingent on the unity of movements. This is a complex, if not equivocal definition of individuation. In rejecting both hylomorphism and atomism, the first attributing individuality to matter and form and the second attributing individuality to the basic elements of nature, Descartes thus provides an alternative interpretation: An individual body is that which has a solitary, simultaneous movement of corpuscles.38 He thus avoids grounding individuality on substantiality. Individuality is not intrinsic to natural bodies, but is a consequence of their modal variation. Movement and figures shape bodily diversities and provide individuation to them. The question of individual bodies arises as an issue connected to instantiation. Movement provides coherence and unity to matter, transforming parts into portions of a singular body. In article 31, Descartes confirms this issue by claiming that “each body has only one proper motion, since it is understood to be moving away from only one set of bodies” (Principia philosophiae, II, art. 31, AT VIII-1 57; CSM I 236). While demonstrating the relativity of motions in a body, Descartes also raises the argument of the unity of a specific body. The appropriate example is that of a ship. As several motions occur in the ship (the wheels of the watch, the walking of a man, and so on), the ship remains one and the same. Whether it moves or is at rest, a ship has a coherent body and proper motion. As Frédéric de Buzon and Vincent Carraud have underlined, “determining the proper movement entails the determination of the individual body” (de Buzon and Carraud 1994: 83–84),39 and the case of the identity of the ship is meaningful. From article 37 to article 52, Descartes presents the three laws of nature and the application of these rules on bodies, not particularly different from Le Monde.40 What interests me is what happens next. In making a general qualification about the applicability of these laws, Descartes suggests the necessity to “inquire into the difference between fluid and solid bodies” (Principia philosophiae, II, art. 53, AT

Original Latin is: “Ubi per unum corpus, sive unam partem materiae, intelligo id omne quod simul transfertur [. . .]. Et dico esse translationem, non vim vel actionem quae transfert, ut ostendam illud semper esse in mobile, non in movente.” Cf. Reid 2014; Brown and Normore 2020: 25–62, and esp. 38–51. 38 Cf. Grosholz 1994. de Buzon 1995. Slowik 2001. Alexandrescu 2009. Toth 2022. 39 Cf. de Buzon and Carraud 1994: 90. 40 For a reconstruction of these articles, see Gaukroger 2002: 114–130. 37

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VIII-1 70; CSM I 245 [translation modified]).41 This resides in the fact that “fluids are bodies made up of numerous tiny particles which are agitated by a variety of mutually distinct motions; while hard bodies are those whose particles are all at rest relative to each other” (Principia philosophiae, II, art. 54, AT VIII-1 71; CSM I 245). In this sense, the difference between them consists in the mechanical structure of their parts: Fluids offer no resistance to bodies entering them, and for this reason, they are moving bodies, while solids do resist and are stationary. Bodily cohesion and unity thus depend on the relationship between particles and their ability to move. In sum, in reducing qualities to extended matter and to the mechanics of movement, Descartes achieves the individuality of bodies and the mechanical possibility to study them in their own right. Still, Descartes’s attempt to describe the real, actual world in Part 2 of the Principia needs something more, as he aims to use the abstract laws of physics to explain various features of the real world.42 In this sense, Descartes should bridge his theory of matter and the mechanics of motions of Part 2, and the knowledge of particular bodies of the next parts of the Principia, namely applying the laws of nature to the study of cosmology, chymistry, and biology. The study of particular bodies thus emerges as a significant feature, philosophically necessary in his late physics. While this exigency was limited in Le Monde, in the Principia the knowledge of phenomena appears entailed in the premises of his physics—namely in the real existence of the world of bodies proved in article 1. This results in a precise physical enterprise.

3.3

Describing Natural Particulars: The Visible World

At the beginning of Part 3 of the Principia, Descartes aims to put his project forward by explaining all the phenomena of nature. This is possible by “examin[ing] whether these principles alone [which derived from the light of reason] enable us to explain all natural phenomena ” (Principia philosophiae, III, art. 1, AT VIII-1 80; CSM I 248). Discussing the perception of something through sensation might appear inconsistent in Descartes. Yet, as I discussed in Chap. 2 of this book, Descartes’s methodology allows for a combination of a priori and a posteriori knowledge. This combination especially works in his physics, as he necessarily deals with external nature. However, this takes different forms. In Le Monde, Descartes makes an original appeal to observation, as he uses the physiology of human vision to confirm that the mental construction corresponds to the actual world, as I show in a moment. Still, this attempt does

Original Latin is: “prout sunt dura vel fluida: quorum ideo diversitas in quo consistat, hic est quaerendum.” 42 From a metaphysical point of view, Descartes built this bridge at the end of Meditation 5 and in Meditation 6, but in the Principia he tackled this issue from a physical perspective. 41

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not bridge the gap of his early physics. In the Principia, Descartes adds a physical bridge to this gap, revealing how to apply the principles of his physics and the abstract laws of physics to explain particular bodies.43 In this case, insofar as one does not aim “to deduce an account of causes from their effects” (Principia philosophiae, III, art. 4, AT VIII-1 81; CSM I 249) but moves from the principles defined in Part 2, observation and experimentation help fill in the knowledge of particular bodies, and as I have shown earlier, also the construction of hypothesis helps in explaining phenomena. In this section, I discuss the role of observation in Descartes’s knowledge of nature, as it takes diverse forms throughout his works on physics.

3.3.1

Observation in Le Monde

Descartes’s 1629 and 1630 correspondence with Mersenne contains several references to a few observations of celestial phenomena. In October 1629, Descartes informs his correspondent that he is interested in explaining all sublunary phenomena, as he is examining with order the whole of meteorology.44 A month later, his intention grows into accounting for all the phenomena of nature, the whole of physics.45 Accordingly, Descartes’s intuition is that the equation he applied to explain a singular phenomenon works to account for nature as a whole. As is well known, Descartes moves from the explanation of the rainbow he observed in a flask of water, where he made a ray of light pass through it. This equation concerns optics, but he later applies it to nature.46 Despite his observations, and besides the methodical interpretation of observations, Descartes does not ground the physics of Le Monde on observation.47 Yet, observation plays a role in his early physics. This is connected to L’Homme, his early physiological text, which originally constituted the last chapter of Le Monde. Accordingly, Descartes adds this physiological explanation of animal 43

My interpretation is that the gap between the construction of a theoretical model and the knowledge of the actual world that one experiences in the study of particular bodies leads to the mind–body gap. In this part of the Principia, Descartes applies to physics the bridge he had laid down in the Meditationes. 44 Descartes to Mersenne, October 8, 1629, AT I 22–23; CSMK 6. On the meteorology of Le Monde, see Brissey 2012. 45 Descartes to Mersenne, November 13, 1629, AT I 70; CSMK 7. 46 Cf. Schuster 2000. See also Martin 2011: p. 129 on the divergence between the mathematical explanation of the rainbow and the attempt to discuss meteorology only using matter and local motion. 47 It should be noted that Le Monde as we possess it today is not the volume projected and written by Descartes. In 1637, he extracted from his early physics two essays and prepared them for publication, namely La Dioptrique and Les Météores. This also occurred to L’Homme, which was published only posthumously in 1664 as a separate text. In 1632, Le Monde ou Traité de la Lunière probably had a very different shape, with a different scientific significance.

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sensation, and more specifically, of vision, as he aims to describe man as a spectator of nature.48 While L’Homme appears as a problematic work in many respects, the fact that it mostly deals with sensation and the nervous connection with the brain has scientific significance. This physiological explanation helps him to verify the knowledge of nature and the way we know nature as a construction of the mind. In revealing the consistency in the mechanical construction of men observing light and nature,49 Descartes thus bridges the gap between the mechanical explanation of the new world and the sensation we have of light and bodies in the old world. In this way, and only at this moment, both worlds coincide. In observing the spectacle of nature, man confirms he sees nature as mechanized by the laws described in Le Monde. In this sense, observation confirms and verifies physics. The result is striking. Despite Descartes’s invention of nature as a construction of the mind, he felt compelled to add an empirical confirmation of it, by expounding the ways one sees, perceives, and knows nature. Yet, a question remains: Is the world visible? And, if visible, how can one know particular bodies? Descartes does not make this last step in his early physics. To solve these questions, one should investigate Descartes’s Essais, and more specifically Les Météores, a text entirely devoted to sublunary phenomena.

3.3.2

Les Météores and the Rainbow

Les Météores is the second of the three essays of his method and concerns the study of the bodies between the earth and the sky. The first essay is entitled La Dioptrique and concerns geometrical optics and physiological optics.50 These features are related. While in La Dioptrique, Descartes explains the activity of vision, in the following essay, he puts vision into practice as he analyses the bodies one observes in the sky. A connection results: Since vision follows the geometrical rules described in La Dioptrique, the phenomena one perceives should follow the same rules. In this reduction of nature to geometry, the second essay discloses Descartes’s challenges to traditional physics. First, he rejects wonder, traditionally conceived as the first moment of knowledge, to which he opposed a science constructed on the principles of nature, extension, and motion. In reducing natural bodies to the mechanization of nature, Les Météores contains Descartes’s rejection of Aristotelian real qualities and his anti-hylomorphism in the study of physics.51 Descartes explores sublunary, natural phenomena, starting from vapors and exhalations, then

Cf. Le Discours de la Méthode, V, AT VI 42; CSM I 132: “and finally about man, because he observes these bodies.” On the status of Descartes’s early physiology, see Alban-Zapata 2016. Baldassarri 2023a. 49 See Le Monde, XIII, AT XI 151; G 124. See Baldassarri 2022a, b, c. 50 Cf. Cimino 1990. 51 Cf. Petrescu 2015. 48

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he investigates salt, discussing whether “it is possible to know the forms of bodies that philosophers claimed to be composed by elements following a perfect mixture, and those of meteors, which they claimed to be composed only as an imperfect mixture” (Les Météores, I, AT VI 232 [translation is mine]).52 Then, he explores winds, clouds, rain, hailstorms, snow (and especially the hexagonal snowflakes), rainbow, and the phenomena related to light in the sky. He starts his explanation by means of several physical hypotheses or suppositions, which reiterate the principles of physics expounded in Le Monde. First, he supposes that: [a] water, earth, air, and all the bodies around us are composed of little parts of diverse shape and size, whose disposition [allows for] a few gaps; [(b), he] suppose[s] that these gaps are not empty, but are filled of a very subtle matter, disseminating the action of light. [c] Then, in particular, [he] suppose[s] that the little parts composing water are long, smooth, and slippery as little eels [. . .] and could be easily separated. In contrast, [d] the parts of earth, air, and the majority of bodies have irregular and diverse figures and would easily interconnect as the branches of hedges. (Les Météores, I, AT VI 233 [translation is mine.])53

As in Le Monde, Descartes claims that little particles or corpuscles of matter compose the various bodies. The arrangement of particles produces their variety. Accordingly, when particles strongly join, these compose bodies as hard as the earth, wood, and similar bodies, while when they merely lean on one another, they compose liquids such as oils or air.54 What differentiates these bodies is the interconnection of these particles. When they firmly join together, for example, the pores of hard bodies do not allow subtle matter to fill the gaps, so “we perceive marbles and metals to be colder than wood,” (Les Météores, I, AT VI 235) as the most subtle particles of light less easily fill them. In sum, the perceivable qualities of bodies, as well as the passages of states (liquefaction and so on) entirely depend on the arrangement and the interactions between particles.55 Yet, in comparing the diverse modes shaping matter to the “infinity of modes [shaping] stones with a diverse figure cut from the same piece of rock,” (Les Météores, I, AT VI 239) Descartes claims this interaction is visible and observable.56 In the text, Descartes transfers this system of corpuscles into the macro system of nature, focusing on several sublunary phenomena. He begins Discourse 2 of Les Météores by claiming that the presence of subtle matter in the pores of terrestrial bodies is what makes vapors and exhalations, namely those bodies whose shapes and

52

Cf. Descartes to Mersenne, March 1636, AT I 340. On salt see paragraph 4.3.2 in this book. Cf. Descartes to Plempius for Fromondus, October 3, 1637, AT I 422; CSMK 65. Descartes to Reneri for Pollot, April or May 1638, AT II 43; CSMK 101. 54 Les Météores, I, AT VI 234. 55 Cf. Les Météores, I, AT VI 236: “pour le froid et le chaud, il n’est point besoin de concevoir autre chose, sinon que les petites parties des corps que nous touchons, étant agitées plus ou moins fort que de coutume, soit par les petites parties de cette matière subtile, soit par telle autre cause que ce puisse être [. . .] cela cause en nous le sentiment de la chaleur; au lieu que, lorsqu’elles agitent moins fort, cela cause le sentiment de la froideur.” 56 Les Météores, I, AT VI 238. See Chap. 4 of this book. 53

3.3

Describing Natural Particulars: The Visible World

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Fig. 3.1 Nature and meteorological phenomena. In René Descartes, Les Météores, II, AT VI 242

figures allow them to move in a certain way, to rise. This occurs “neither for any particular inclination [of these bodies], nor because the Sun possesses in itself a force of attraction, but only because there is no other place where they could continue their movement” (Les Météores, I, AT VI 240 [translation is mine]). The movements and interactions between particles of matter and subtle matter thus produce a system of vortexes. In Le Monde, this system outlines the movements and characteristics of celestial bodies, in Les Météores, this system illustrates sublunary phenomena and their relations. Descartes provides a figurative representation of nature as a combination of moving matter (see Fig. 3.1). In this representation of nature as a landscape, Descartes depicts the movement of vapors from A to B (this is rarefaction)57 and so on, as particles form clouds (C and D), winds (F and G), and other natural phenomena (D and E).58 Accordingly, nature as a combination of meteorological phenomena is ultimately reduced to the movement and arrangement of particles. Insofar as the explanation of these phenomena relies on inferring the composition and characteristics of bodies from his theory of matter, Descartes thus fleshes out a mechanical reconstruction of nature. What is interesting to note here is that, while his theory of matter grounds this knowledge, Descartes constructs his explanation by means of experimentation and

57 58

Cf. Descartes to Plempius for Fromondus, October 3, 1637, AT I 428. Les Météores, II, AT VI 242–245.

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the observation of nature. This especially surfaces in a few passages of the discourse on salt,59 but it is also evident in many other passages, where he describes the observations and experimentation he has performed.60 More generally, as the representation of nature as a landscape (Fig. 3.1) shows, Descartes watches nature and visualizes the diversities between bodies. In observing these bodies, Descartes claims that his principles produce these effects, thus connecting the visible (observed nature) to the invisible (the corpuscular theory of matter).61 The effects of the interactions of corpuscles are therefore visible in the characteristics of natural bodies. As a result, observation is not just the mere vision of nature but is a scientific experience, previously made true by reason and eased by the construction of instruments of vision, as claimed at the end of La Dioptrique.62 Additionally, in observing nature, the physicist perceives all phenomena as resulting from the movement and interactions of particles, and visualizing the effects of the interactions between particles, the physicist finds confirmation of his theoretical explanation of nature. This circularity grants an ultimate truth to scientific knowledge. This is true for all sublunary phenomena, as the text reveals. Descartes indeed applies his theory of matter and his corpuscularian physics to several natural bodies. An outstanding case is the rainbow,63 which is the subject of Discourse 8 of Les Météores. Daniel Garber and Jean-Robert Armogathe, among several other interpreters, have importantly highlighted the central role of the explanation of the rainbow in the text, as an apt example of Descartes’s methodological application of his principles of physics to nature.64 From an epistemological and methodological perspective, the study of the rainbow perfectly suits the aims of understanding Descartes’s philosophy. He reduces the experience (and wonders) of the phenomenon to a mathematical calculation of the angles of refraction, which he connects to his theory of light. Yet, his explanation starts from common experience, as the rainbow appears in drops of water from a fountain illuminated by the Sun (see Fig. 3.2), later transformed into an experiment. Cf. Les Météores, III, AT VI 253: “Ils mettent du sel mȇlé avec égale quantité de neige [. . .]. Dont la raison est que la matière subtile, qui était autour des parties de cette eau, étant plus grossière, ou moins subtile. . .” Isaac Beeckman gave an account for this experiment in his Journal: III, 190–191. 60 There are at least 30 occurrences of observer/observation or remarquer in Les Météores, while there are at least 10 occurrences of experience in the text (not to say of voir/vision). 61 As Ettore Lojacono has discussed, this is a crucial passage in Descartes. This is evident in his physiology, as well as in his physics. See Lojacono 1996a: 100–102. Cf. Galison 1984; Bellis 2010. 62 La Dioptrique, X, AT VI 226–227. 63 Cf. Descartes to Mersenne, October 8, 1629, AT I 23; CSMK 6: “I had experience of this recently when I was investigating the cause of the phenomenon which you write about [. . .] I had to interrupt my current work in order to make a systematic study of the whole of meteorology. But I think I can now give some explanation of the phenomenon. I have decided to write a little treatise on the topic; this will give the explanation of the colours of the rainbow (a topic which has given me more trouble than any other” and for all sublunary phenomena in general. That is why I asked you for a description of the phenomenon at Rome in particular . . .” 64 Cf. Armogathe 1987. Garber 1993. Armogathe 2000. See also Werret 2001. Buchwald 2008. 59

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Describing Natural Particulars: The Visible World

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Fig. 3.2 Observing the rainbow from a fountain. In Les Météores, VIII, AT VI 344

He achieves this by “mak[ing] a very large [drop of water] so as to be able to examine it better [. . .] [and] fill[ing] a perfectly round and transparent large flask with water” (Les Météores, VIII, AT VI 325; G 85). From the playful nature of the Renaissance and the artificial ability to construct devices reproducing these phenomena (the presence of such devices in Renaissance and early modern gardens was legion),65 Descartes methodologically positions himself as an experimenter. He reconstructs the condition to observe the phenomena by means of experimentation. Therefore, his attempt to deal with the rainbow exemplifies his focus on visible nature as a key element of physics. What results is that, while the explanation of the phenomenon pertains to mathematical calculus (a purely intellectual challenge), an important element of his investigation of nature is the direct observation of it and a question of engineering, that is, a problem of reproducing the phenomenon to observe and study it.66 In studying the rainbow, Descartes thus reduces its size from the macro (the rainbow we see in the sky) to the micro (the corpuscles moving within it) by means of an intermediary body. This reduction to a system we can measure and observe, namely a drop of water in a flask, is meaningful. In moving the globe of water, holding it up to the light of the Sun and placing it in a specific spot, Descartes observes the variations of colors and infers the correct angle of refraction that produced the rainbow (see Fig. 3.3).67

65 Les Météores, VIII, AT VI 344. Cf. Werret 2001: 132–138. See also Beeckman, Journal, I 73–76, 289–290, 293, 361. 66 Cf. Tiemersma 1988. 67 Les Météores, VIII, AT VI 326–329; G 85–87.

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Fig. 3.3 Observing the rainbow from a globe of water made by a flask. In Les Météores, VIII, AT VI 326

As a result, he applies his mathematics and his theory of light to an observation constructed in his laboratory, adding experimentation to his reasoning. The result is the knowledge of an outstanding physical phenomenon. Later, to figure out the appearance and order of colors, Descartes performs another experiment with an artificial glass or a prism, through which he makes a ray of light pass. The combination of observations with reason (mathematical reasoning, theory of matter, and theory of light) appears as a relevant aspect of his investigation of natural bodies, at least in the case of the rainbow.68 While observation makes him visualize a specific case, and while bridging the gap between artificial and natural, his methodological study of nature allows him to extrapolate the explanation of a singular phenomenon and apply it to all natural particulars. In this case, the explanation for the drop of water works for all natural raindrops, even the little one far in the sky. Yet, this is made possible by observing nature, even if reconstructed in a laboratory. In paving the way to the understanding of particular phenomena and to the study of natural bodies at large, the visualization of nature as an interaction of corpuscles is therefore a suitable condition for achieving Descartes’s physics. Nature and particular bodies are ultimately visible—and the objects of scientific observation.

68

Les Météores, VIII, AT VI 334; G 90: “reason agrees so well with observation.”

3.3

Describing Natural Particulars: The Visible World

3.3.3

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A History of Natural Phenomena: Observed Nature in the Principia

Descartes entitles Part 3 of the Principia “De mundo adspectabili” [The visible world]. As already discussed in Chap. 2, in article 4 of this part, he claims the necessity to make a short history of natural phenomena to be explained in these parts of the text. Yet, what this history consists of is unclear. Parts 3 and 4 of the Principia have a very different structure than Le Météores and outline the formation of celestial and terrestrial bodies, ultimately expounding their characteristics. Still, no history of nature in the traditional sense surfaces in these parts, although Descartes provides a universal history of the heavens and describes some particular cases. Accordingly, the observation of natural phenomena becomes the ground to isolate the case for his investigation. In this sense, natural history is thus a survey of the visible effects, that is, the visible bodies, which he should order within reason. In article 6, Descartes states that observation is not merely sensory perception—the latter was reduced to the knowledge of beneficial and harmful in Part 2—but it should be combined with reason and mathematical calculation,69 that is, be theoretically grounded. This is what occurred in Les Météores, where vision is theoretically framed. In the latter text, Descartes confirms that nature is visible and, in this sense, observations are the way to achieve scientific knowledge and confirm that his theory of matter works on natural bodies and particular phenomena. Similarly, in the Principia, Descartes starts from what is observed, such as the “appearances of the planets [Planetarum apparentias]” (Principia philosophiae, III, art. 15, AT VIII-1 84; CSM I 250 [translation modified]).70 As Lojacono has claimed, Descartes’s way of proceeding in science “starts from experience [. . .] as it helps determine the field of investigation of physical studies” (Lojacono 1996b: 429–430). In both Les Météores and the Principia, this experience consists of the visualization of nature. A difference from Les Météores, however, surfaces. In the Principia, the hypotheses one proposes to explain celestial bodies should account for the appearances one perceives in the skies. This is the innovative perspective of the text—innovative in the Cartesian philosophy of nature. While Descartes’s ultimate aim is to explain all celestial phenomena by means of the principles of his physics, he follows a different path from his early works. In the earlier parts of the Principia, he has already stated the principles of knowledge and the principles of physics, therefore showing that his theory of matter is certain and true. Yet, in Part 3, he starts from what one observes in the sky, the appearances of celestial bodies. The visible nature therefore surfaces as the substratum to which one should apply his theory of matter and his corpuscular physics in order to know it. As a result, Descartes does not infer the existence of natural bodies from the laws of nature, as he does in Le Monde, and somehow in Les Météores, but moves from the appearances of bodies, that is, from observing them as

69 70

Principia philosophiae, III, art. 6, AT VIII-1 82: “Agnoscimus etiam, visu ratione adjuto. . .” Cf. Ibid., art. 16, AT VIII-1 85; CSM I 250.

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they are, to which he applies his corpuscular physics. The visualization of natural bodies is therefore the point of departure for studying them. This reveals a much more traditional path. Let us focus a bit on the different ways of investigating nature in these three texts. In Le Monde, Descartes invents nature as a construction of the mind. Nature is a geometrical construction, and since no account of particular bodies surfaces, he combines this rational physics with actual nature by means of man as a spectator. In Les Météores, Descartes describes a few particular phenomena by means of his physics (which in the texts are called hypotheses) as he lays bare such suppositions, and then infers that what we observe in meteorological events (actual nature) derives from his corpuscular physics. In the Principia, he starts from the appearances of the body and phenomena (actual nature), whose existence is metaphysically grounded, and through the observation of phenomena he explains these effects by applying the principles of his theory of matter. While in Le Monde nature is constructed by the mind, and in Les Météores, natural phenomena are immediately perceived as a movement of corpuscles, in the Principia, nature is given, and a physical investigation starts from the universe (and its bodies) as it appears. Indeed, Descartes entitled Part 3: De mundo adspectabili [the visible world]. In all these cases, the ground for scientific knowledge is corpuscular physics (namely his matter theory) and nature is, in the end, nothing but extended matter, whose essence is known in reason. Yet, in the Principia, observation does not serve to verify physics, as it occurs in Le Monde, but to provide physics with an object of investigation. This combination of visible nature as a point of departure to acquire science later surfaces in article 203 of Part 4 of the Principia. At this stage, Descartes claims that, as it happens with “men who are experienced in dealing with machinery [and who] take a particular machine whose function they know and, by looking at some of its parts, easily form a conjecture about the design of the other parts, which they cannot see. In the same way I have attempted to consider the observable effects and parts of natural bodies and track down the imperceptible causes and particles which produce them” (Principia philosophiae, IV, art. 203, AT VIII-1 326; CSM I 289). Descartes thus claims that he has started from visible nature and applied his physics to these effects (therefore not inferring knowledge from the effects to the causes) as nature and natural phenomena are observable and, by means of his physics, explainable.

3.4

Conclusion

Descartes devoted great attention to the knowledge of nature, i.e., his physics, the trunk of his natural philosophy according to the well-known image he provided. While his interpretation of nature as extended matter never changed, he adjusted his physics to several questions connected to his philosophy. In this chapter, I have tried to highlight a few crucial passages. The first is Descartes’s definition of nature as extended matter, whose only attribute is extension in length, breadth, and depth. Nature is a piece of matter made of corpuscles indefinitely divisible (which denies

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Conclusion

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the existence of atoms) and filling the whole of space (which denies the void), and whose only differentiation pertains to their extension and motions. Undoubtedly, this is a mechanical interpretation of nature. Moreover, corpuscles move and take diverse figures and shapes, which are the modes of extended matter, as Descartes strips nature of all the qualities and forms, forces, and virtues of the philosophical traditions, and ultimately conceived nature as a geometrical space. Indeed, the motions of aggregates of corpuscles forming bodies could be expounded by means of mathematics. As a result, the laws of nature (which are laws of motion) reveal the composition and differentiation between bodies. In showing how these corpuscles interact, these laws account for the qualities of all bodies, making the knowledge of particular bodies possible. This definition of nature is consistent with Descartes’s epistemology, both in the sense that its knowledge is grounded in reason and in the sense that in the Regulae he had reduced natural variety to a grey ontology, in which all bodies are ultimately equal. This point, however, entails a few questions. One is to combine physics with nature, that is, how one could apply his corpuscularian theory with the knowledge of the diverse, particular bodies. In this chapter, I have discussed the ways in which Descartes tried to deal with this issue. In the course of his philosophical enterprise, Descartes has dealt with physics and particular bodies from different perspectives. In the first section of this chapter, I discussed Descartes’s invention of nature in Le Monde. In the earlier text, he presents nature as a construction of imagination (i.e., a rational construction). Physics is thus true because it is a production of the reason. Yet, an identification between the world within the mind (the imagined nature) and the actual world should be verified by observation, but no investigation of particular bodies surfaces in his early physics. In Sect. 3.2, I discussed the ways one could account for particular bodies in Descartes’s rationalistic physics, by means of the laws of nature. Especially in Part 2 of the Principia, in which he laid bare the principles of material objects, Descartes discusses in detail his theory of matter and theory of motion, ultimately revealing the mechanization of nature. In Sect. 3.3 of this chapter, I uncovered the attempt to connect his physics (namely his theory of matter and theory of motions) with the study of particular bodies, the phenomena of nature. Observation made this connection possible. Yet, a different connection between physics and nature and a different way of observing nature fascinatingly surface at different stages of his works. While in the project of Le Monde Descartes uses observation to confirm that the nature imagined is the actual nature, in the later works, this interpretation changes. In both Les Météores and the Principia, Parts 3 and 4, Descartes accounts for observed, particular bodies. More precisely, he deals with the observed universe to which he applies the abstract laws of his physics. What results, however, is that an investigation of natural particulars is possible within Descartes’s mechanical reduction of nature to extended matter. As he writes at the end of the Principia: “It seems that all the other phenomena, or at least the general features of the universe and the Earth which I have described, can hardly be intelligibly explained except in the way I have suggested” (Principia philosophiae, IV, art. 206, AT VIII-1 329; CSM I 291). Methodologically constructed on a scientia

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grounded in the mind, Descartes’s mechanical physics (nature as extended matter and laws of motions) intelligibly accounts for all particular bodies populating the universe, ultimately explaining nature as a whole. In the next chapters, I investigate how much this intelligible explanation of nature works in his attempts to deal with the study of metals, plants, and animals.

Chapter 4

Metals

Abstract Since the late 1620s, Descartes engaged with the study of stones, rocks, minerals, and metals, performing several observations and experiments to establish his knowledge of nature consistent with his philosophical program. In this sense, he firmly rejected alchemy for its ungrounded principles, false notions, and uncertainty, although he praised chymical experimentation, which he performed in order to achieve some knowledge of particular bodies. Throughout the time, he not only studied the qualities of mixtures such as salt, minerals, metals, and magnet, but also dealt with particular, strange cases, such as fossils, miraculous and floating rocks, or the Bologna stone, ultimately producing a sound mechanization of mineral bodies in Part 4 of his Principia philosophiae. In this chapter, I disclose several diverse cases that emerge in both his correspondence and works, especially laying bare the limitations and riches of the reduction of chymistry to his mechanical physics. While observations and hypotheses play an eminent role in Descartes’s investigations of metals and minerals, the metaphysical and physical principles of the Principia allow him to provide a more philosophically established mineralogy. Likely in November 1627,1 René Descartes attended a meeting in Paris, or in La Rochelle, to listen to a lecture arranged by papal nuncio Guidi di Bagno. The speaker was a chymist named Nicolas de Villiers, sieur de Chandoux (?–1631), who presented a new alchemical philosophy that challenged Aristotelian and scholastic traditions.2 While the talk was enthusiastically received by the audience—which included Mersenne, Morin, Villebressieu, and others—Descartes criticized Chandoux’s philosophy as merely probable. In the summer of 1631 letter to

1

The date and location of this meeting are anything but certain. Recently, Theo Verbeek has tried to shed light on these issues, suggesting that the meeting did not occur after the fall of La Rochelle in October 1628, and it is very likely it took place in La Rochelle. I follow Geneviève Rodis-Lewis’s interpretation, in Rodis-Lewis 1995: 101-ss. A different interpretation is in Stephen Gaukroger, who followed Baillet’s interpretation that the event took place in December 1628, see Gaukroger 1995: 183-ss. 2 See Joly 2011: 64. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 F. Baldassarri, René Descartes’s Natural Philosophy and Particular Bodies, Studies in History and Philosophy of Science 60, https://doi.org/10.1007/978-3-031-48663-0_4

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Villebressieu, Descartes wrote a short report of the meeting of 1627, recalling how much he “made the whole company recognize what power the art of right reasoning has [. . .] and how much better founded, and more true and natural, [his] principles are than [Chandoux’s]. You were as convinced as everybody else, and you were all good enough to beg me to put them [Descartes’s principles] in writing and to publish them” (Descartes to Villebressieu, Summer 1631, AT I 213; CSMK 32). Indeed, besides the rejection of the alchemist’s philosophy, something more surfaces. As Richard Popkin and Stephen Gaukroger noted, this meeting was a pivotal event in the philosopher’s development,3 as it spurred Descartes to refine his philosophy and to propose the principles of a new system of nature, especially focusing on metals, minerals, and stones, the main subject of Chandoux’s talk.4 More recently, Bernard Joly has claimed that this meeting (1) sparked Descartes’s rejection of the alchemical study of nature and (2) triggered the development of his own natural philosophical program. Regrettably, Descartes did not elaborate on this meeting any further nor did he put his principles in writing, as he promised in the early 1630s. Still, the letter to Villebressieu discloses three relevant points. First, Descartes acknowledged that Villebressieu’s chymical work would “help to disabuse poor sick minds concerning the adulteration of metals [les sophistications des métaux] on which you have worked so hard and to so little effects, without having found any truth in the idea in twelve years of assiduous work and numerous experiments.” Second, Descartes praised Villebressieu’s discovery of a mechanical composition and arrangement of different elements, reducible to particles, which “constitute the animal or the plant or the mineral.” Finally, Descartes claimed that this interpretation “suits [his] style of philosophizing very well, and it accords admirably [merveilleusement] with all the mechanical experiments which I have performed upon nature in this field” (Descartes to Villebressieu, Summer 1631, AT I 216–217; CSMK 32–33 [emphasis in the text]). Besides the disparagement of alchemy, this letter reveals Descartes’s attention to the knowledge of natural bodies and the claim that from chymical experimentation, it is possible to infer a mechanical understanding of nature as an arrangement of particles. This is consistent with his own natural philosophy, making it operative in the study of stones, rocks, metals, and minerals.

3 4

Popkin 1979: 175. Gaukroger 1995. Cf. MacDonald 2002: 448–454. See Matton 2013. Cf. Baillet La vie de Monsieur Descartes: vol. I, 160–165.

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In these years, Descartes’s attempt to explain all sublunary phenomena consisted of studying the qualities of natural bodies,5 the weight of metals,6 and the performance of a few experiments with metals,7 as Descartes’s epistolary exchange with Mersenne shows.8 The Stockholm inventory lists under item E a table on the weight of metals, two folia entitled “Ex[certpa] Kircheri de Magnete,” and two folia with a “history of metals” (Stockholm inventory, AT X 8–9) that Descartes likely worked on in the late 1620s or early 1630s. However, this study does not constitute a separate section of his philosophy. In a brilliant passage of a 1632 letter to Mersenne, Descartes confirmed that “after the general description of the stars, the heavens and the earth,” namely his cosmological section of physics, he had then added a discussion of the “substantial forms [of particular, terrestrial bodies]. This is what has occupied me these last days; for I have been making various experiments to discover the essential differences between oils, ardent spirits, ordinary water and acidic liquids, salts, etc.” (Descartes to Mersenne, April 5, 1632, AT I 243; CSMK 37 [emphasis added]). The knowledge of the essence of terrestrial bodies appears to be connected to cosmology, and therefore to physics, but it also derives from experimentation. Despite this claim, this topic is absent in Le Monde, as I have highlighted in Chap. 3. In this chapter, I aim to engage with Descartes’s approach to stones, minerals, and metals. This investigation outlines an important part of Descartes’s epistolary, composes a crucial section of his natural philosophy, especially Part 4 of Principia philosophiae, and significantly intersects his study of living nature—in 1630, Descartes claimed he was working on the intersections between chymistry [chimie] and anatomy.9 Although Joly’s work has suitably explored this field with great care of detail, in this chapter, I shed new light on this section of Descartes’s philosophy of nature, beyond Joly’s restricted focus on the differences between Descartes’s studies and seventeenth-century chymistry. Albeit Descartes did not encompass these studies within a chymical knowledge, but reduced any possible chymical approach to his physics, it is to be noted that the French philosopher conceived the Earth as a great chymical laboratory to understand natural bodies, as suggested by Joly, therefore

5 Cf. Descartes to Mersenne, January 1630, AT I 109: “6. Je vous remercie des qualités que vous avez tirées d’Aristote; j’en avais déjà fait une autre plus grande liste, partie tirée de Verulamio [namely, Francis Bacon], partie de ma tête, et c’est une des premières choses que je tâcherai d’expliquer, et cela ne sera pas si difficile qu’on pourrait croire; car les fondements étant posés, elles suivent d’elles-mêmes.” Descartes is likely speaking of Aristotle’s De Generatione et corruptione, Book 2, Chapter 2, while more problematic is the reference to Bacon—possibly, the reference is Francis Bacon’s De augmentis scientiarum, III, 4 or even the Phoenomena universi, whose manuscript circulated in Europe. 6 Cf. Descartes to Mersenne, December 18, 1629, AT I 97; Descartes to Mersenne January 1630, AT I 113–114. 7 Cf. Descartes to Mersenne, February 25, 1630, AT I 123. 8 On Descartes’s interest in all sublunary phenomena, see Descartes to Mersenne, October 8, 1629, AT I 23. 9 Cf. Descartes to Mersenne, April 15, 1630, AT I 137.

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performing chymical experimentation and combining the latter with the application of the geometrico-mechanical principles of his physics. In this sense, he was in fact a reductionist but was much more interested in the observations of phenomena as generally recognized. As a result, Descartes’s mineralogy outlines a meaningful and rich attempt to bridge the gap between his metaphysics and the natural philosophical study of particular bodies. In Sect. 4.1, I outline Descartes’s rejection of alchemy, and his appreciation of the chymical experimentation, whose practical interest was recognized, but which was of small use without a clear theory.10 In Sect. 4.2, I investigate his study of stones, and especially the Bologna stone and other wonders that emerge in his correspondence. In Sect. 4.3, I explore his description of qualities in Le Monde, which paves the way to his definition of nature as extended matter, and the study of salt, a paradigmatic case of the application of the method and the role of experimentation as a point of departure to flesh out the principles of his physics. In Sect. 4.4, I discuss Descartes’s explanation of minerals and metals in the universal history of the Principia. In Sect. 4.5, I present his interpretation of the magnet. In embedding the study of minerals within the principles of his mechanical physics, a complex picture of Descartes’s philosophy surfaces, as he relied on observations, experimentation, and suppositions to describe the properties and variety of mixtures.

4.1

The Rejection of Alchemy

Descartes’s refusal of alchemy cannot be overstated. In the first part of Discours de la Méthode, he wrote a harsh criticism of superstitious and false sciences, which one may explore to “guard against being deceived by them” (Discours de la Méthode, I, AT VI 6; CSM I 113), and then specifically affirmed that: for the false sciences, I thought that I already knew their worth well enough not to be liable to be deceived by the promises of an alchemist or the predictions of an astrologer, the tricks of a magician or the frauds and boasts of those who profess to know more than they do. (Discours de la Méthode, I, AT VI 9; CSM I 115)11

Yet, in Regulae ad directionem ingenii, Descartes’s position over alchemy appears more conflicting. First, he differentiated between magic and astrology, as he referred to them as absurd disciplines, while the transmutation of metals has a

10

In this chapter, following the current interpretation to express inclusively the undifferentiated domain, chymistry is used when it refers to a specific scientific endeavor, whereas alchemy is used when Descartes referred to the more esoteric study of nature. Indeed, Descartes used the two terms interchangeably to refer to the theories he condemned or to the practices he performed and repeated, but he also used the term alchemist to label some of his contemporaries. See Principe and Newman 1998 and 2001; Joly 2007 and 2013. 11 In relation to this text, Joly adds that the madmen of the first Meditation are alchemists. See Joly 2011: 45, n.1.

4.1

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position among the sciences of his method.12 On the other hand, in Rule 4, he fleshes out that “almost every chemist [Chymistae], most geometers, and many philosophers pursue their research” directing “their mind down untrodden paths, in the groundless hope that they will chance upon what they are seeking” (Regulae ad directionem ingenii, IV, AT X 371; CSM I 15–16). Then, Descartes acknowledges that “they sometimes are lucky enough in their wanderings to hit upon some truth,” but then adds an important specification, according to which it is far better to follow a methodology in order to acquire knowledge rather than “walking in the dark,” as these people generally do (Regulae ad directionem ingenii, IV, AT X 372; CSM I 16). While in the Discours, he grouped astrologists, magicians, and alchemists together, in the Regulae, he differentiated between them. He rejected some practices generally connected to alchemy, whereas he also affirms that chymical activities such as the transmutation of metals (Rule 1) could lead to some knowledge (Rule 4), although what the alchemists promise to attain is difficultly achieved (Rule 4 and Discours). In other words, restricted to his methodological framework, Descartes praises some chymical performances, namely those related to the experiential study of nature. In the letter to Villebressieu, Descartes praised his friend’s experiment with metals as a way to (1) observe nature and (2) build a physics clear and certain, but also (3) to disenchant those who believe in the sophistication of metals, i.e., in the obscurities of alchemists. Accordingly, chymical experimentation helps shed light on the nature of bodies if one does not attribute it too much power over nature, that is, if one does not expect to infer too much knowledge from it. Descartes clearly rejected the occult dark side of alchemical knowledge, which he considered philosophically ungrounded and methodologically uncertain, as in the case of Chandoux’s philosophy.13 In a 1629 letter to Mersenne, Descartes wrote that “as soon as I see the word arcanum in any proposition I begin to suspect it” to be uncertain knowledge (Descartes to Mersenne, November 20, 1629, AT I 79; CSMK 11 [emphasis in the text]). Yet, this does not entail that he was uninterested in a chymical study of nature. For the moment, let us focus on Descartes’s criticism against alchemists and alchemy. In 1637, Descartes wrote to Mersenne that he “mock[ed] the fantasies of the chemist of whom you write, and believe that such chimeras are unworthy to occupy the thoughts of a decent man [honnête home] for a single moment” (Descartes to Mersenne, ca.20 April 1637, AT I 351; CSMK 54 [translation slightly modified]). In 1639, Descartes claimed that the aims of the one who wanted to “demonstrate religious mysteries by means of chemistry” (Descartes to Mersenne, August 27, 1639, AT II 573) were similarly ridiculous. According to Joly, in this case, Descartes likely referred to Pierre-Jean Fabre’s (1588–1658) Alchymista 12

On astrology and magic, see Regulae ad directionem ingenii, VII, AT X 398. It should be noted that this section is absent from the Cambridge manuscript of the Regulae, generally conceived as a former version of the text. On the transmutation of metals, see Regulae I, AT X 360. 13 I am not dealing with Descartes’s proximity with Rosi-Crucian sect, nor with his travels in Germany, in which he might have encountered other alchemists. See Joly 2013: 52–61. Mehl 2019b.

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christianus (1632), in which the author aimed to interpret everything by means of alchemical philosophy. Descartes considered unacceptable the claim that the whole of nature could be explained by means of alchemical principles. In October 1640, Descartes was informed by Huygens of a recent book published in The Hague, a “book composed by a charlatan [. . .] against you” (Huygens to Descartes, October 8, 1640, AT III 761).14 This book is Pentalogos in Libri cujusdam Gallico idioate evulgati quatuo discursum: De la methode, Dioptrique, Meteorique, & Geometrique (1640), written by a mysterious Mercurius Cosmopolita (namely Andreas of Habernfeld).15 This book contains a chymical attack against Descartes’s Discours de la Méthode and Essays. Descartes knew the name of the author, “a Bohemian chemist living at The Hague,” who, according to him, “has done [to him] great honor, for having claimed to have said the worst possible things [about Descartes], in fact he has said nothing that could touch [Descartes himself]” (Descartes to Mersenne, December 3, 1640, AT III 249 [translation is mine]).16 The book attracted some attention, as it opposed Descartes’s mechanical interpretation of nature by means of the alchemical theory and principles, also charging Descartes of reviving atomism, a common criticism at the time.17 Thus, Habernfeld offered a chymical alternative to Descartes’s mechanical explanation of natural bodies, mostly revealing how much an alchemical outline fails to communicate with Descartes’s interpretation. Descartes did not reply to Habernfeld’s criticism and conceived the Pentalogos as a dangerous book for any attempt to attain scientific knowledge and unworthy of any further attention. Yet, in 1640, Descartes’s correspondence features another interesting case in this regard. The exchange between Descartes, Lazare Meyssonnier (1611/1612–1673), and Christophe de Villiers (c. 1585-c. 1650), in which Mersenne operated as an intermediary, contains some important details.18 While the main topic is their challenges to Descartes’s theory of the conarium, the epistolary also deals with some alchemical features, as both had practiced chymical experimentation. For instance, Villiers had informed Mersenne about distillation from plants, while Meyssonnier practiced some alchemical experiments related to his medical work, which he published in Pentagonum philosophicomedicum (1639), a text Descartes had harshly criticized for mixing astrology, chiromancy, and other silliness.19 In a July 1640 letter to Mersenne, Descartes affirmed that Meyssonnier’s “discourse on Sel Aërien, and on the difference between vital and animal spirits, which 14

Cf. Descartes to De Wilhem, October 5, 1640, AT III 201. Recently, Erik-Jan Bos has identified Mercurius Cosmopolita as Andreas Haberweschel von Habernfeld (1587-before 1660). Cf. Bos 2023. 16 Original French is: “C’est un Chimiste Bohémien, demeurant à La Haye, qui me semble m’avoir fait beaucoup d’honneur, en ce qu’ayant témoigné vouloir dire de moi tout le pis qu’il pouvait, il n’en a rien su dire qui me touchât.” 17 See Roux 2000. 18 On Meyssonnier, see Trevisani 1979. Meschini 1998: 37–47. Trabucco 2018. On Villiers, see Biasiol 1981. 19 Descartes to Mersenne, January 29, 1640, AT III 15. 15

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[Meyssonnier] compared to Elemental Fire and Aerial Mercury, [. . .] overcome [s] my capacities [of understanding], which also means, entre nous, that I consider these things anything but unintelligible stuff, whose solely utility is to gain admiration from ignorant people” (Descartes to Mersenne, July 30, 1640, AT III 120 [translation is mine]). In a few pages later in the same letter, Descartes dealt with Villier’s text (of which Mersenne had likely made some excerpts to him) claiming that Villiers’s “fixed spirit [Esprit Fixe] appears no more intelligible than speaking of dark light or hard liquor” (Descartes to Mersenne, July 30, 1640, AT III 124 [translation is mine]), thus highlighting a crucial oxymoron in Villier’s. Additionally, in speaking of alchemical principles, namely salt, oil, and sulfur, which Mersenne called the principles of chymists, Descartes stresses that: these principles are nothing but false imagination, grounded on the fact that in their distillations, [Chemists] extract waters that constitute the more slippery and collapsible [déliées et pliantes] parts of the extracting bodies, and they reduce them to mercury. They also extract oils, whose parts are branchy shaped [. . .] and relate it to sulfur; and they relate to salt the most fluid [déliées] parts that remain, which could be mixed with, and be incorporated in water; finally, the most coarse parts [. . .] are their Caput mortuum or Terra damnata, which is a useless matter for them. For what remains, I neither conceive of such indivisible parts, nor any difference among them apart from the diversity of their figures. (Descartes to Mersenne, 30 July 1640, AT III 130–131 [translation is mine])

In this letter, Descartes utterly rejects the chymical principles of both Meyssonnier and Villiers, claiming that the bodies they refer to are not the principles of nature, but a construction of false imagination. Accordingly, alchemists conceive salt, mercury, and sulfur as the tria prima, or the elemental principles of nature, something that Descartes suggests is the mere result of distillation. In this sense, their difference only pertains to their mechanical figure, which is indefinitely divisible— this is one of the principles of his matter theory. Since matter is infinitely divisible, it cannot be reduced to elements such as mercury, sulfur, or salt—nor to atoms. As a result, these bodies cannot be the principle of nature, as claimed by alchemists. Similarly, what alchemists call caput mortuum, namely the remains of distillation, could “be entirely reduced in salt, water, oil, and in subtle matter if one grinds or concocts with some solvents” (Descartes to Mersenne, September 15, 1640, AT III 180 [translation is mine]), according to Descartes.20 Even in this case, Descartes claimed that no indivisible matter subsists, as any element could be further reduced to particles. Finally, in an October 1640 letter, he writes to Mersenne that Villiers’s alchemy is nothing but a variant of Aristotelian philosophy, as one should add substantial forms and real qualities to understand the transmutation of bodies proposed by Villiers without changing anything in the end.21 Several years later, Descartes fleshed out his rejection of alchemy in a letter to the Marques of Newcastle (William Cavendish, 1592–1676). In November 1646, he wrote that: 20

On caput mortuum, see Crosland 2006: 81. Descartes to Mersenne, October 28, 1640, AT III 211–212. On Aristotelian mineralogy, see Eichholz 1949. 21

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I agree entirely with your Lordship's judgement about the chemists. I think they use words in an uncommon sense only in order to make it seem that they know what in fact they do not know. I think also that what they say about reviving flowers with their salts is only an idle fancy, and that the powers of their extracts are quite different from the virtues of the plants from which they are taken. This is clear empirically because wine, vinegar and brandy, three extracts made from the same grapes, have quite different tastes and powers. In my view, the chemists' salt, sulphur and mercury are no more different from each other than the four elements of the philosophers, and not much more different from each other than water is from ice, foam and snow. I think that all these bodies are made of the same matter, and that the only thing which makes a difference between them is that the tiny parts of this matter which constitute some of them do not have the same shape or arrangement as the parts which constitute the others. I hope that your Lordship will soon be able to see this explained at some length in my Principles of Philosophy, which is about to be printed in French. (Descartes to Newcastle, November 23, 1646, AT IV 569–570; CSMK 302)

In highlighting that alchemy entails obscurity, ignorance, deception, and false imagination, and in suggesting a similarity between the tria prima and the scholastic four elements, this letter sums up the content of Descartes’s criticism against the chymical doctrine of his time. Against it, Descartes suggested reducing the differences between bodies to the shapes, figures, and arrangement of particles, namely to his own mechanical philosophy, ultimately affirming that he could account for all mineral variations by means of his mechanical physics. This work is ultimately collected in 1637 Les Météores and in 1644 Principia philosophiae, whose French translation was published in 1647. Before investigating this work, it is important to note that, while a direct challenge to the principles of alchemy develops in Descartes’s correspondence, his rejection of chymical experimentation is less prominent. On the one hand, he claimed that the alchemical definition of elements (i.e, the tria prima) is inconsequential and obscure, but on the other hand he was more attentive to the chymists’s experimentation with mineral bodies. In his correspondence, Descartes referred to concoction, distillation, and other alchemical activities such as plant palingensis, as something he himself performed or tried to observe, despite obtaining very different results in comparison to those of alchemists. He praised the experimentation of chymists, such as the one of Villebressieu, which he encompassed within his own method to be effective, as a way to study stones, minerals, and metals. In the next sections, I discuss these observations of natural bodies and the ways Descartes applied his principles of physics to the mineral world.

4.2

Between Wonder and Observations: The Bologna Stone and Other Curious Cases

Since late 1629, Descartes started performing observations and experimentation on minerals. As he wrote to Mersenne, “for what concerns your experiments, I find iron heavier than copper, but the difference is tiny; and since I found some rust on the former, I believe that the rust adds weight to the iron. I leave it to get rustier, to see

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whether it will be heavier” (Descartes a Mersenne, December 18, 1629, AT I 97 [translation is mine]). In February 1630, he thanked Mersenne for a table with the weight of metals, but then added “to be unable to infer any conclusions from these, except that it is very difficult to perform accurate experiments in this field” (Descartes to Mersenne, February 25, 1630, AT I 123; CSMK 19). Although little is known about such table, this is likely the one contained in Mersenne’s Harmoricorum libri XII (1636) and in the Harmonie Universelle, contenant la théorie et la pratique de la musique (1636), where he included a table with the weight and the specific weight of materials. In these months, Descartes performed a few observations on metals, as he claimed in April 1630.22 He weighted metals and observed their differences, and from these observations, he engaged with Mersenne’s table. For instance, he claimed that for Mersenne “gold is lighter than lead [. . .] [or] pure silver to be as heavy in water as in air, and bronze heavier, which is impossible,” for this is “the very opposite of what [Descartes] clearly find[s] to be the case” (Descartes to Mersenne, February 25, 1630, AT I 123; CSMK 19). What Descartes exactly did is sometimes unclear. Likely, he approached these issues focusing on the movement and arrangement of particles composing the body, that is, on their internal structure, as it emerges in his correspondence with Meyssonnier and Villiers. This investigation is consistent with the definition of Regulae ad directionem ingenii, in which he had claimed that, in dealing with the body, one knows a few entities such as the extension, the figure, and the movement, which constitute the qualities of bodies.23 In observing these features, Descartes provided a study of the heaviness, hardness, and other qualities of bodies consistent with his mechanical physics. For instance, in discussing transparency, he wrote to Mersenne that “most small bodies looked at through lunettes [i.e., microscopes] appear transparent because they are in fact transparent, but many small bodies placed together are not transparent, because they are not joined together in a uniform way, and since the parts are not uniform, their arrangement is enough to make opaque what was originally transparent. You can see this from a piece of glass or candy: these are no longer transparent when they are crushed, even though each part of them is transparent” (Descartes to Mersenne, January 1630, AT I 109; CSMK 17–18). In this short passage, three main aspects of Descartes’s philosophical approach to inert bodies surface. First, experimentation grounds this study, as he performed observations by means of magnifying glasses. Second, he investigated the structure of bodies to uncover their qualities such as transparency (and one could extend this approach to hardness, heaviness, and all other qualities). Third, what specifies these qualities is the arrangement of particles, that is, their extension and shape: In the case of transparency, this depends on their uniform arrangement, while, if one crushes them, their particles rearrange and lose transparency. Although he embedded this knowledge within the principles of his physics, the study of the qualities of bodies proceeds a posteriori. First, he observed the structure

22 23

Descartes to Mersenne, 15 April 1630, AT I 141. Regulae ad directionem ingenii, XIV, AT X 440.

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of one body; then, he derived further qualities (such as transparency); and finally, he connected these qualities to geometrical and mechanical principles. The knowledge of inert bodies moves from the observations of effects to the definition of causes. A year later, in October 1631, Descartes wrote to Mersenne that from several experiments he had developed the rejection of void, and an explanation of “heaviness, lightness, hardness, etc. [. . .] in two chapters that I promised to send you at the end of the year” (Descartes to Mersenne, October or November 1631, AT I 228; CSMK 33). Resulting from observation, this explanation is in Le Monde, and it is the topic of the next section of this chapter. Before discussing Le Monde, in this section I would like to explore Descartes’s correspondence a bit more, especially because it contains a few examinations of strange mineral phenomena and curiosities that generally attracted the interest of early modern erudite scholars. These curiosities consist of unique bodies or strange experiments with a peculiar result. Although in many cases Descartes could not offer a complete explanation of the phenomenon under investigation, these reveal the ways he applied his method to know such phenomena, as he aimed at reducing them to his philosophical program. A first case concerns the experience performed by a certain Samuel van der Straten. Constantijn Huygens wrote to Descartes about van der Straten’s claim to be able to “melt an oriental diamond or gold (which he claims will result into a sort of yellow quicksilver) in the palm of [his] hand, or some other metal, except [. . .] lead and copper [. . .] by means of a little corrosive substance one could keep on his own tongue.” While Huygens expected to attend this performance soon, and while several Jesuits considered it utter charlatanism, he asked Descartes’s opinion on this case, insofar as the latter possessed “this science” (Huygens to Descartes, July 30, 1638, AT II 668–669 [translation is mine]), according to Huygens. Descartes’s reply is illuminating. I report it in its entirety. For what concerns Mr van der Straten’s philosophy, I find it unusual, but I do not judge it impossible. Common acqua fortis [namely, nitric acid] dissolve metals, but wax could resist them. Equally, they easily dissolve iron and steel, while quicksilver dissolves gold, tin, and lead, though it can hardly fix itself on iron or copper, or even less on non-metallic bodies. The reasons could be easily imagined for those who know that bodies are composed of little parts differently united and with different sizes and shapes. For example, beating glasses or earthenware with a stick, one could shatter them, but using the same stick against wool or hay will not produce any change [. . .]. So it is not impossible to imagine a body, whose parts move in a certain way that makes them operating against the parts of gold [. . .]. Yet, it is strange that a same body helps melt gold and diamonds. Since [van der Straten] offers you to prove [this], I think [. . .] it would be enough if he could dissolve a piece of common glass. In common glass there is enough crystal soda [salicot dans le cristallin] that the sole humidity of the air could melt it. Yet [. . .] his secret is rare and you should know it. (Descartes to Huygens, 19 August 1638, AT II 671–672 [translation is mine])

In this text, Descartes is aware of the corrosive capacities of nitric acid or aqua fortis.24 Still, he incorrectly mixes the operations of acid and mercury or quicksilver,

24

Cf. L’Homme AT XI 121.

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as Joly has importantly highlighted.25 Both are dissolutions, although the second is more correctly an amalgam. Despite the mistake, this reveals how much Descartes was aware of the properties of quicksilver and how much he performed experiments with it. The second aspect is that he compared these chymical operations to the crushing of a body into tiny parts, for bodies are composed of such little parts whose arrangement follows different shapes or figures—this is consistent with his previous explanation of transparency. Consequently, the quality of all bodies relies on the arrangement of particles. This is a very mechanical explanation of chymical operations—and Descartes reduced van der Straten’s philosophy to his mechanics. Within this mechanical system, it is possible to conceive the existence of a body that dissolves gold without affecting other metals or minerals, but Descartes claimed it is difficult to imagine that such a body operates on diverse minerals. Finally, Descartes found van der Straten’s odd claim to have developed a dissolvent through which he could cut prison bars and suggested Huygens to acquire some knowledge about it. In this letter, Descartes spelled out his mechanical understanding of chymical operations: The mechanical arrangement, shape, and figures of the particles of bodies help specify their chymical qualities one could observe through the series of experiments performed by van der Straten. What remains unknown is the latter’s secret, which Descartes recommended Huygens to acquire, although it is likely that this effect depends on the presence of specific matter in glass, according to Descartes. Another case is in an October 1640 letter to Mersenne in which Descartes discusses the “difficulties concerning the parts of metals that float in aquafortis.” He affirms that these parts of metals “mix and permeate in the parts of aquafortis, as these latter are eased in their movement [. . .] differently from the powder that does not float” (Descartes to Mersenne, October 28, 1640, AT III 210 [translation is mine]). The reason of their floating resides in their structure and in the movement and arrangement of particles. Descartes’s explanation appears consistent with his mechanical physics. A few months earlier, Descartes used a similar explanation to expound the case of “the stone floating in vinegar” which Mersenne had sent him. Descartes performed several observations of it, as he “plunged it in vitriol, where it moved more than in vinegar” (Descartes to Mersenne, June 11, 1640, AT III 80 [translation is mine]). His explanation is that: [the stone] has several pores that easily accommodates the parts of such liquors, but have not the figure to accommodate the parts of fresh water, nor those of other liquors [. . .] and that the parts of vinegar enter the pores in the bottom part of this stone, making air or water exit in a way that make these pores expand (as it is proved by the little boiling phenomena around the stone), agitate, and raise; in consequence of this, the stone must plunge to the bottom of the plate, as it does. (Descartes to Mersenne, June 11, 1640, AT III 80–81 [translation is mine])

In observing this phenomenon, Descartes provides a mechanical explanation of the stone whose floating is due to the shape of its pores that allow the entrance of the parts of vinegar. Subsequently, these particles push the parts of water and air already

25

Joly 2011: 77–78.

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present within the stone, making it float for a while. Similarly, Descartes discusses the case of bread that “attracts water,” which depends on the fact that: the pores of such bread are bigger than the particles of air, and subtle matter enters these pores, surrounds the parts of air and make them revolve more rapidly than how they do outside the pores. Now, since all bodies move aiming at leaving the places where they are, when such particles of air get out from the pores touching the surface of water, the parts of water enter and replace air [. . .]. Something similar occurs in the most part of burnt bodies or in calcination. (Descartes to Mersenne, June 11, 1640, AT III 83–84 [translation is mine])

Accordingly, the attraction of water is due to the arrangement of particles and to the laws of motion: As particles move freely, the parts of air contained in bodies are forced to move by subtle matter and forced to leave their seat, while this space is occupied by other particles with a different shape, better fitting the pores of bread. Correctly speaking, this is not an attraction, but a mere replacement of matter pursuant to the qualities of extended matter, utterly consistent with Descartes’s mechanical physics. Moreover, Descartes affirms that subtle matter does not “enlarges pores indifferently, but only those that are inclined [disposé] [. . .] like those of a bended bow, and not those of gold, lead, etc” (Descartes to Mersenne, June 11, 1640, AT III 86–87 [translation is mine]). The question is what inclination means in this case. Yet, in suggesting that inclination is regulated by the fact that “these [pores] are too tight in the one part, and too broad in the other part” (Descartes to Mersenne, June 11, 1640, AT III 87 [translation is mine]), Descartes made clear that he was speaking of a mechanical arrangement of parts. Against the claim of mysteries or magic powers in nature, Descartes reduced the qualities of bodies to the mechanical laws of his physics. All qualities and characteristics, as well as all phenomena, could be explained through the modes of extended matter, namely the motion, arrangement, figures, and shapes of particles composing the bodies. In this way, Descartes could explain the accretion of minerals in caves, as I investigate later, and the fossilization of woods, about which Mersenne asked Descartes in two letters dated October and November 1639. In his reply, Descartes followed the mechanical framework of his natural philosophy. This theory is rapidly sketched in a 1637 note of the Excerpta anatomica, where Descartes specified that as metals grow by an apposition of particles, fossilization “of wood or other bodies” consists of “this kind of growth, as the parts of stones enter the pores of wood, and in this way they assimilate the other parts [namely, those of woods], or expel them” (Excerpta anatomica, AT XI 596 [translation is mine]). In the 1639 letters to Mersenne, Descartes discussed the “caves in Rome where stones change into woods” (Descartes to Mersenne, October 16, 1639, AT II 595 [translation is mine]), a curious phenomenon in which stones could have a resemblance to wood without being wood. In November 1639, Descartes stated that the fact that “stones look like dark wood [. . .] has nothing extraordinary,” for there are “areas in Brittany, where I saw stones of this nature” (Descartes to Mersenne, November 13, 1639, AT II 619 [translation is mine]). Since before 1635, members of the Italian Accademia dei Lincei were attracted by the phenomenon of fossil wood in Acquasparta, close to Rome, where some stones still resembled wood not yet fossilized, as Francesco Stelluti’s (1577–1653) Trattato del legno fossile minerale nuovamente scoperto

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(1637) presents. Likely, Mersenne was referring to this case with Descartes, who claimed this is a kind of fossilization that could be explained through the mechanical framework of his physics, and no mysteries or curiosity should be attributed to such a case—similarly, no miraculous condition should be attributed to stones depicting saints, whose figure solely depends on the arrangement of particles.26 The last case concerns the Bologna stone, an emblematic phenomenon in the early modern period. This stone originates in the alchemical laboratory of Bolognese cobbler-alchemist Vincenzo Casciarolo (1571–1624), who performed a few alchemical operations of calcination on a shining stone he had found on the nearby slopes of Monte Paderno. The result of such operations was a luminescent stone that glowed at night after being exposed to the Sun. Originally thought to be the philosopher’s stone, this object attracted the attention of naturalists and philosophers, as the phenomenon of mineral luminescence lagged unattainable.27 Conceived as either an object of collection or a subject of cosmological explanation, it was at the center of a lively debate between scholars. For instance, Niccolò Cabeo claimed that the stone attracts the light as magnet does, in Philosophia magnetica (1629), while Ovidio Montalbani, in De illuminabili lapide bononiensi epistola (1634), and Fortunio Liceti, in Litheosphorus sive De lapide bononiensi (1640), claimed that the stone belongs to the Moon, in opposition to Galielo’s cosmology. In 1641, the anonymous correspondent Hyperaspiste raised this example to challenge Descartes’s metaphysical claim that no creatures could be kept in being without a continuous action of God, just as light would disappear if the Sun stopped shining.28 Descartes replied that “in the Bologna stone the light of the Sun is not preserved, but the Sun’s rays kindle a new light which can afterwards be seen in shadow” (Descartes to X***, August 1641, AT III 429; CSMK 193 [translation slightly modified]). In describing this case, Descartes rejected his correspondent’s claim to use a body (however peculiar as it might be) as a model for the entire nature and to hypothesize a diverse substantial form for each body. Moreover, he rejected the idea that God is not the cause of all existing nature, as “there can be no sunlight without the Sun” (Descartes to X***, August 1641, AT III 429; CSMK 193 [translation slightly modified]). While there is no direct explanation of the phenomenon per se, because he did not observe it and explaining its phenomenon would be difficult—in 1646, Descartes wrote to Colvius that he “only had hearsay about the Bologna stone; [and] never saw it, and would be very reckless to explain it” (Descartes to Colvius, October 5, 1646, AT IV 517 [translation is mine])—this surfaces as an example to confirm a few metaphysical and physical principles. The latter are the impossibility to access infinity (namely God) through a finite body; the unity of the thread of causation (i.e., any luminescence derives from the Sun); and the mechanical physics of light,

Cf. Descartes to Mersenne, June 19, 1639, AT II 557–558, “l’ombre du corps de St Bernard qui paraît sur une pierre . . .” 27 See Newton Harvey 1957. Gomez 1999. Taddia 2004. Taddia 2009. Baldassarri 2014. Principe 2020: 21-ss. 28 X*** to Descartes, July 1641, AT III 405. Cf. Meditationes de prima philosophia, AT VII 369. 26

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whose mechanical laws are universal and nothing represents an exception to them. Nevertheless, a discrepancy emerges between the metaphysical and physical principles on the one hand, which he could provide, and the explanation of the nature of the stone on the other hand. Without observing the stone, Descartes could confirm his principles of philosophy but remained unable to expound its phenomenon of luminescence from these principles. While discussing rarities and curiosities, magic and miraculous stones, Descartes’s application of his mechanistic physics to natural bodies slowly surfaces in his correspondence, insofar as his explanation follows the modes of extended matter, namely the movement, arrangement, shapes, and figures of particles composing these bodies. Still, he acquired this knowledge a posteriori, that is, from observations and experiments, and not a priori from the principles of his philosophy—ultimately, he confirmed the latter through the former. The case of the Bologna stone is particularly meaningful in this sense, for although Descartes used it to flesh out the universal validity of his principles of philosophy and physics, he cannot explain the phenomenon of this stone from these principles. As I show in the next section, this itinerary from the observation of bodies to the principles characterizes the study of particular bodies in both Le Monde and Les Météores.

4.3 4.3.1

The Qualities of Particular Bodies and Salt in the 1630s The Qualities of Bodies in Le Monde

As Descartes claimed to Mersenne in 1632, the chymical experiments of the early 1630s on the nature of salt, oils, aqua fortis, and so on, as well as the study of heaviness, hardness, transparency, and other qualities of bodies, should compose his early physics, namely Le Monde. However, as I have discussed in Chap. 3, Le Monde has a quite complex structure, and it contains little descriptions of particular bodies. In the text, Descartes did not expound all bodies or qualities, as promised, but mostly provided a theoretical framework to the observations of these qualities he had performed in those years. Indeed, he shows how much the explanation of some qualities established on experimentation is consistent to his mechanical definition of nature as extended matter, ultimately shaping a theory to encompass the knowledge of inert bodies.29 This is an important issue, as Descartes first discussed a few qualities aiming to show that these cannot be expounded following the Scholastic system (i.e., the identity between sensation and things), but only by reducing them to the motion and arrangement of particles. From this explanation of bodily qualities, he then laid

29

Cf. Le Monde, AT XI 9; G 8.

4.3

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out a theory to encompass this reduction, that is, the famous definition of nature as extended matter regulated by the laws of motion. Let us focus on a few cases. In Chapter 3 of Le Monde, for instance, Descartes illustrates hardness and fluidity, exploring “the difference between bodies that are hard and those that are fluid.” This difference does not reside in some Scholastic qualities, but in the arrangement of their particles, as “every body can be divided into extremely small parts [. . .]. I detect no difference [. . .] except that the parts of the one can be separated from the whole much more easily than those of the other. Thus, to make the hardest body imaginable, I think it would be enough for all the parts to touch each other, with no space remaining between any two and none of them [. . .]. For what glue or cement can one imagine [. . .]?” (Le Monde, AT XI 13; G 10). Accordingly, what specifies the hardness of bodies is the arrangement of particles, and not some internal quality: The more particles are connected, the less they would move and be separated, and the more a body is hard. In contrast, in a fluid body, all particles are freer to move. No other differences is allowed, according to Descartes, who then added that “this judgment [opinion] is corroborated by [all experiences] I have cast my eye on” (Le Monde, AT XI 14; G 11), as he likely referred to the observations discussed in his correspondence. Furthermore, by means of these observations, Descartes investigates how much bodies change their state and lose their hardness, and what produces such changes. For example, as he describes in the text, fire renders bodies fluid: “when it melts metals, it acts with a power not different from that by which it burns wood. But because the parts of the metal are all approximately equal [in size], it cannot move out without the other, and consequently it forms completely fluid bodies from them” (Le Monde, AT XI 14; G 11).30 This text contains two important claims. First, Descartes is here discussing a chymical operation—the melting of metals in furnaces—reducing it to the movement and arrangement of particles. Second, his task is to account for the traditional four elements as four states of a body, therefore reducing such differences to extended matter. In appealing to, and likely performing chymical experiments, Descartes explained the combustion of solid bodies as a destruction of the arrangement of their internal structure, which produces different results according to the original arrangement of particles: Metals liquefy completely, for example, while wood produces different substances. Another case of bodily transformation occurs through liquefaction by acids. Similarly to the discussions in his correspondence, in Le Monde, Descartes affirms that if one pours some acids or aqua fortis on metals, these fluids move and separate the parts of such bodies, dissolving these bodies.31 Descartes’s reduction of such operations to his mechanical physics allows him to reject the Scholastic natural dispositions of bodies, as he claims that either burning or melting is caused by elements operating on the arrangement of hard bodies, therefore producing different results according to the differences of the original arrangement of bodies.

30 31

See also note 23 in that page. Le Monde, AT XI 15; G 12.

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Yet, what remains unexplained at this stage is what specifies the nature of fire or the nature of acids in causing such transformations. Descartes described these activities by means of the infiltration of particles of fire and acids into solid bodies, where they move, separating particles, but he fails to explain why such bodies are either melted by fire or dissolved by acids. At the end of Chapter 3, he claims that “the power to burn,” as well as, likely, the power to dissolve, pertains to the fact that particles “move much more quickly” (Le Monde, AT XI 16; G 12). What clarifies this point a bit is the discussion of elements contained in Chapter 5 of Le Monde, where Descartes starts fleshing out the definition of nature as extended matter. An important passage of Chap. 5 of Le Monde is indeed where Descartes invites the reader to “examine [. . .] the forms that can be given to mixed bodies by the various motions, the various shapes and sizes, and the different arrangement of the parts of matter” (Le Monde, AT I 27, G 19). This is a turning point in Descartes’s physics, for he summarizes his previous investigations by claiming that all qualities could be reduced to the motion, shapes, sizes, and arrangements of particles, which he later defines as the modes of extended matter. What is important to note is that the earlier parts of Le Monde are not grounded on this definition of nature, but mostly relies on the direct experimentation and observations with bodies, which Descartes likely performed in the early 1630s. In this sense, the chymical experiments with metals and minerals help pave the way to his geometrico-mechanical physics and to the definition of its principles and laws of motions. Nevertheless, given the absence of any further discussion of particular bodies in the text, a salient lacuna seems to emerge between the chapters in which the author explains bodily qualities—grounded on observation—and the definition of nature as extended matter, which is established on a mathematical inference. Despite being consistent with these principles, the knowledge of particular bodies mostly relies on chymical experimentation, and not on an a priori definition of nature as extended matter. In the following chapters of Le Monde, Descartes mostly deals with cosmology, and nothing else surfaces on minerals and metals.

4.3.2

Salt in Descartes’s Philosophy

Despite its absence in Le Monde, salt is a significant case, to which he devoted some attention, as Descartes claims in several letters to Mersenne. For instance, in writing on a May 19, 1635, letter to Jacob Golius (1596–1667), Descartes reported that he had “not yet had the time to put sea water to the test to see whether [he] could discover what the cause of its light is” (Descartes to Golius, May 19, 1635, AT I 318; CSMK 48).32 This is a particular case of marine luminescence that was not an uncommon topic of investigation at the time, as it surfaces in Bacon’s and

32

See Verbeek 2013.

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Beeckman’s works, among others.33 Not differently from his contemporaries, Descartes connected this question to the presence of salt in water, and thus to the nature of salt. In an (unfortunately) undated note of the Excerpta anatomica collected in the section entitled Problemata [Problems], Descartes investigates “why the power of heat [vi caloris] cannot extract salt with the rest of water?” (Excerpta anatomica, AT XI 621 [translation is mine]). According to Descartes, the solution does not reside in the transparency of salt, as someone has proposed, because water is transparent too. Accordingly, what prevents salt from evaporating is that, “because of its dryness,” salt “is penetrable [pervium] by the movement of heat,” while water could be penetrated by the movement of light, but cannot by the movement of heat because of its humidity, and this could explain “why seawater sparkles at night” (Excerpta anatomica, AT XI 622 [translation is mine]).34 Connected to the claim that salt does not evaporate, Descartes affirms that fruits and meat are not salty, as “the Sun does not raise [salt] in plants,” because salt is “immovable [fixum]” or inflexible, and it is also “very dry [while] only glutinous things compose the flesh” (Excerpta anatomica, AT XI 622 [translation is mine]). As a result, what characterizes salt is dryness, solidity, and fixity, all qualities depending on the arrangement of its particles. Descartes developed these points in Discourse 3 of Les Météores, entitled “On Salt,” a very paradigmatic text for probing into Descartes’s mechanical interpretation of nature.35 He moved from the movement of vapors, the subject of Discourse 2, to focus on the properties of seawater and all the qualities of salt. The ground of this explanation is the mechanical difference between bodies that he provided earlier in the text as a hypothesis—as seen previously in Chap. 3— according to which the diversity of figures and sizes and the diverse arrangement of particles form different bodies with diverse qualities.36 Following this hypothesis, Descartes defined salt as formed with big particles that cannot be folded but are oblong like sticks whose extremities are equal and inflexible particles.37 This is proved by the taste of seawater, which is more stinging than sweet water because its particles cannot be fold by subtle matter and sting the tongue,38 and also by the fact that, if the particles of salt were different, “they will sink,” or “cannot easily exit 33

An ancient topic, see Aristotle, Meteorologica II, 2–3, 355a–b, 357a–358b. Cf. Beeckman, Journal, I, 96–97. 34 Cf. Descartes to Mersenne, April 30, 1639, AT II 531. 35 Cf. Hattab 2019: 134. 36 Les Météores, I, AT VI 233–236: “je me serve, au commencement, de quelques suppositions, ainsi que j’ai fait en la Dioptrique [. . .]. Je suppose, premièrement, que [. . .] tout les autres tells corps qui nous environnenet, sont composes de plusieurs petites parties de diverses figures et grosseurs. . .” 37 Les Météores, III, AT VI 251: “qu’elles [i.e., the particles of salt] sont également grosses par les deux bouts, et toutes droites, ainsi qu’autant de petits bâtons. . .” 38 Les Météores, III, AT VI 250. As Helen Hattab has shown, this is a geometrical principle applied to sensed objects. Cf. Hattab 2019: 136.

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[from water]” (Les Météores, III, AT VI 251 [translation is mine]). As a result, Descartes’s explanation of the nature of salt derives from his experience and not from an a priori definition of the properties of salt. Grounded on this mechanical explanation of seawater, Descartes could indeed expound all its qualities. For instance, he could explain why water and salt could unite, which depends on the fact that “the parts of salt, remaining transversally extended the one on the other, give room to the parts of water, which are perpetually agitated, to wrap and coil around the former, arranging in an order in which [the latter] could continue move [. . .] as if they were alone” (Les Météores, III, AT VI 251 [translation is mine]). Even the dissolution of salt into water, which occurs as a result of the fact that “folding parts of water could embrace [salt], and coils around it” (Les Météores, III, AT VI 252 [translation is mine]), has a mechanical explanation. Later, Descartes explains why seawater is heavier and more transparent that sweet water,39 how to obtain ice in summer, and why sweet vapors arise from seawater, but also more particular cases, such as why seawater is more salty at the Equator than at Poles, or why seawater is less apt to extinguish fires, or why it produces new fires.40 The text continues with Descartes’s investigation of several other properties of seawater and salt. In all these cases, he reduces these qualities to the arrangement, sizes, and movement of particles of salt. Then, he investigates the diverse figures that salt takes—sometimes showing it through the help of illustrations.41 As a result, no quality is beyond understanding: salt dryness, solidity, fixity, and also its explosive power or the fact it easily dissolve in fire, its friability, and its white color and transparency, could all be explained by means of his mechanical physics.42 Finally, he deals with what alchemists call salt spirit or oil [esprit ou huile de sel], namely an extremely strong and sour water they claim could dissolve gold,43 which is the result of an alchemical extraction. Accordingly, the parts of this sour water are the same that composed the salt before the extraction, but since they could not arise through the alembic, the power of fire changes their shape, figure, and qualities, from cylindrical to flat and sharp, without changing their nature. The change of their geometrical shape also entails why this body tastes differently from salt, as Descartes explains. Descartes’s mechanical physics efficiently outlines the nature of salt and the properties of seawater. Yet, while this knowledge is grounded on the hypothesis of extended matter composed of particles, Descartes’s explanation develops from the observations and experiments with seawater and salt he had performed throughout the time, as reported in the text, and the definition of salt as composed of oblong and

39 It is to be noted that a similar question is in Aristotle’s Problems, cf. Aristotle, Problemata 932b 8–9. 40 Les Météores, III, AT VI 255. This is a similar phenomenon to the fire produced in stones. 41 Les Météores, III, AT VI 257–262. 42 Les Météores, III, AT VI 262–263. 43 Les Météores, III, 263–264. Cf. Joly 2013: 127.

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inflexible particles is proved by these experiences. In this sense, moving from observed properties and particular cases, Descartes confirms that the essence of salt consists of oblong shaped particles, therefore moving from effects to causes, as discussed by Hattab.44 As a result, the chymical experiments he had performed throughout the years play a crucial role in paving the way to his explanation of salt and particular bodies, ultimately confirming the mechanical principles of his physics. Two readers of Les Météores challenged Descartes’s mechanical interpretation of salt, as testified to his correspondence. The first is Libert Froidmont (1587–1653), who significantly rejected Cartesian mechanization of nature. Froidmont had published an Aristotelian text on the meteors, namely Meteorologicum libri sex (1627), and when he read Descartes’s rebuttal of species intentionales and substantial qualities in favor of corpuscles, he claimed that such a reduction of qualities to particles is unintelligible and fails to account for bodies.45 This concerns both the difference between heat and cold, which according to Froidmont could not reside in the “local movement [but] in the qualities [of bodies] that touch the organ” (Fromondus to Plemp for Descartes, September 3, 1637, AT I 407 [translation is mine]), and the taste of seawater, which could not merely depend on the arrangement of particles.46 According to Aristotelian metaphysics, quantity is an accident of a substance and does not depend on the mechanical arrangement of corpuscles. Against Descartes, Froidmont reinstated Aristotelian real qualities.47 What made Cartesian mechanization unintelligible for Froidmont is the absence of the principles in Descartes’s philosophy, a striking objection insofar as Descartes himself had claimed he hid his principles, and the reader could subsequently think that this philosophy falls back on the physics of Epicure. In challenging this criticism in a December 1637 letter to Vopiscus Fortunatus Plempius (or Plemp, 1601–1671), Descartes states that: sizes, shapes, positions, and motions are my formal object (in philosophers’ jargon), and the physical objects which I explain are my material object. The principles or premises from which I derive these conclusions are only the axioms on which geometers base their demonstrations [. . .] but they are not abstracted from all sensible matter, as in geometry, but applied to various observational data which are known by the senses and indubitable. For instance, from the oblong and inflexible shape of the particles of salt, I deduce the square shape of its grains, and many other things which are obvious to the senses. (Descartes to Plemp, December 20, 1637, AT I 476; CSMK 77)48

The modes of extended matter, namely arrangement, size, figure, and motion, are the principles Descartes relies on in explaining inert bodies and all the phenomena Hattab 2019: 136: “[Descartes] sought to a priori demonstrations but gave confusing (to both Plempius and us) examples in his attempt to persuade readers, through a posteriori reasoning.” 45 Fromondus to Plemp for Descartes, September 3, 1637, AT I 406: “this composition of bodies from parts of different shapes seems excessively crass and mechanical.” 46 Fromondus to Plemp for Descartes, September 3, 1637, AT I 408. 47 Cf. Verbeek 2014: 69–83. See also, Garber 1988. Martin 2011. Martin 2013. 48 On the claim that his physics is nothing but geometry, see Descartes to Mersenne, July 27, 1638, AT II 268. 44

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related to them, as the case of salt has highlighted. Without any need of Aristotelian real qualities or substantial forms, Descartes’s mechanical explanation of particular bodies appears consistent to his interpretation of nature as extended matter: Quantity is essential as one may deduce real properties from the geometrico-mechanical principles of nature, which he applies to sensible (material) objects, as he claimed with Plemp. Yet, as his letter to Plemp suggests, Descartes alludes to a broad hypothetico-deductivist method in which he proves these notions (namely the arrangement, sizes, and figures of salt) by means of the observations deployed in Discourse 3. In this sense, instead of explaining the effects (the microstructure and properties of salt) by the causes (his corpuscularian theory of matter), he aims “to demonstrate the cause by the effects a posteriori” (Descartes to Plemp, December 20, 1637, AT I 476; CSMK 77). As a result, Descartes’s explanation of salt (as well as his entire meteorology) follows an a posteriori demonstration, from effects observed by means of experimentation back to the causes and principles—and in a certain sense this is consistent to his study of qualities in Le Monde, as seen before. This not only illuminates the role chymical experimentation played in Cartesian study of minerals and particular bodies, but also reveals a gap in his program. The second reception is in a letter Pollot wrote to Reneri in February 1638. Pollot stressed that Descartes’s mechanical reduction of tastes and other powers to the figure and shapes of particles resulted in absurd consequences, such as that “bodies with the same figures will produce the same [taste], despite being insipid,” or “the power of salt to preserve things [. . .] only consists in its figure,” or that “having this figure [. . .], it will be easy to desalinate water by merely filtering it” (Pollot to Reneri for Descartes, February 1638, AT II 516 [translation is mine]). Pollot’s appeal to real qualities and substantial form is less evident than in the previous case, but still important. To this, Descartes replied that: bodies whose particles have the same size, shape, hardness, etc. as those of salt will have the same effect, so far as taste is concerned. That being the case, we cannot suppose that these bodies are tasteless; for something’s being tasteless consists not in its lacking the sensation of taste within itself, but in lacking the power to cause such a sensation. [. . .] Lastly, I do not see why it is held that taste is more an intrinsic quality in salt than pain is in a sword [. . .]. The shape of the parts [of salt] is a contributing factor only in so far as it makes them suited to penetrating the pores of other bodies [and prevent them to rot]. (Descartes to Reneri for Pollot, April or May 1638, AT III 44–45; CSMK 101–102 [emphasis added])

In his reply, Descartes claimed that filtration could work in desalinating water, for the particles of salt could be filtered by a specific body, and seawater loses its taste because it loses the particles of salt, whose shape produces their taste.49 He thus reduced the issue to the geometrico-mechanical framework. In February 1639, Descartes wrote to Mersenne that he could explain “the formation [of bodies] by means of natural causes in details, similarly to the way he explained the formation of a grain of salt [. . .] in the Météores” (Descartes to Mersenne, February 20, 1639, AT II 526 [translation is mine]). And a few months

49

It is to be noted that Bacon maintained that this was possible, in New Atlantis.

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later, he claimed that he performed several experiments mixing salt and water, ice, and snow, as these are quite easy that is impossible to make any mistake.50 According to Descartes, the explanation of salt is a suitable example of his mechanical physiology of inert bodies, through which he aimed at replacing Scholastic philosophy. The latter “explains this matter not very well, as [it] considers puram potentiam, and adds substantial forms and real qualities, namely chimeras” (Descartes to Mersenne, October 28, 1640, AT III 212 [translation is mine]) to their explanation of salt, failing to achieve any sound results. In contrast, the chapter on salt surfaces as a cornerstone to develop a study of minerals consistent with Descartes’s mechanical reduction of nature.51 In 1638, Descartes claimed with Mersenne that, as he explained in his Météores concerning the case of water and salt, the same framework applies to the understanding of the composition of gold, iron, and lead.52 Within this mechanical framework, he could expound some qualities of mineral bodies, such as why “gold is not as hard as iron, though being heavier: [because] its parts [. . .] are not as steadily fastened as [in the latter]” (Descartes to Mersenne, December 6, 1638, AT II 466). Or why iron could acquire more heat than wood without becoming red or burning. Or why tempered iron is harder and more fragile than the non-tempered one.53 Or even why marble is cold and shining, as no particles of light enter it.54 In all these cases, the movement of subtle matter entering the pores of the terrestrial particles composing bodies plays a crucial role in either heating or burning bodies. The effects depend on their structures, but the process is the same. In cooking bricks, for example, the heat tights the pores of bricks originally filled with water, replacing the latter with air, which is lighter, according to Descartes. The mechanical arrangement of particles explains why cooked bricks are lighter than uncooked ones.55 Descartes pointed to his explanation of salt as paradigmatic to his physics in two further epistles. The first is a December 1640 letter in which he wrote to Mersenne that, albeit “not know[ing] the nature of gold enough to determine how its parts move in aquafortis,” he could, however, explain this phenomenon “through the example of salt described in the Météores” (Descartes to Mersenne, December 1640, AT III 256 [translation is mine]) and then listed a few experiments one could perform on this subject. The second is in the letter to Regius in which he replied to Voetius’s criticism sparked by Regius’s theses of the ens per accidens.56 In stressing that the Aristotelian substantial forms may not be used to explain the causes of natural actions, Descartes wrote that “essential forms explained in our fashion, [. . .] give

50

Descartes to Mersenne, April 30, 1639, AT II 530–531. On the explanation of salt as representative of Descartes’s approach to natural phenomena, see Hattab 2009: 126-ss. 52 Descartes to Mersenne, November 15, 1638, AT II 444. 53 Descartes to Mersenne, January 9, 1639, AT II 485–487. 54 Descartes to Mersenne, October 16, 1639, AT II 590–591. 55 Descartes to Mersenne, October 16, 1639, AT II 594–595. 56 Cf. Verbeek 1992a. 51

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manifest and mathematical reasons for natural actions, as can be seen with regard to the form of common salt in my Meteorology” (Descartes to Regius, end of January 1642, AT III 506; CSMK 209). Yet, this claim to mathematical reasons appears mostly rhetorical, for Descartes’s reduction of the nature of salt to geometry does not follow an a priori path, but develops from the observations and experimentation he performed on salt. In sum, the study of salt is a paradigmatic case for understanding Descartes’s mineralogy, and the study of particular bodies in general, as previously seen. The latter is consistent with Descartes’s mechanical physics, for he reduced bodies to extended matter and motion, but he could only derive this knowledge a posteriori from several chymical experiments. A more complete study of minerals and metals composes Part 4 of the Principia.

4.4 4.4.1

A Philosophy of Natural Bodies: The Generation of Mercury, Salt, Oily Natures, Minerals, and Metals A Short History of Minerals

In July 1645, Huygens asked Descartes to send him a treatise on chymical operations, with a “little nomenclature in which you include a great number of Waters, Salts, Oils, Essences, Spirits, Magistères, and other chimerical or superfluous differences that these good people have in their laboratories” (Huygens to Descartes, July 7, 1645, AT IV 779 [translation is mine]). Descartes declined this invitation, claiming that he has “already given out the little knowledge [. . .] of this subject in the fourth part of [his] principles, when dealing with the nature of minerals and fire and with all the diverse effects to which almost the whole of Chemistry can be related” (Descartes to Huygens, August 4, 1645, AT IV 780–781; translation is from Joly 2013: 131). Adding anything more would possibly lead to errors, “for lack of making experiments necessary to acquire the particular knowledge of each thing” (Descartes to Huygens, August 4, 1645, AT IV 780–781; translation is from Joly 2013: 131). Consistent with his study of salt, Descartes had performed several observations on particular bodies and several effects, which are collected in Part 4 of Principia philosophiae, the topic of this section. The study of natural bodies is part of what he calls “a short history of the principal phenomena of nature” (Principia philosophiae, III, art. 4, AT VIII-1 81 [translation is mine]), which is composed in Part 3 of the study of cosmological bodies and in Part 4 of the study of the Earth and terrestrial objects. These parts are interconnected, as Descartes provided a study of minerals moving from the formation of the Earth and its structure, which he reduced to the combination of particles of matter composing bodies by moving in different ways. This takes the shape of a universal study of natural bodies. This section is, however, a complex piece of Cartesian science.

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Descartes started fleshing out three differentiations between bodies. The first two are geological and concern the history of the parts of the Earth. In the first division (A), Descartes differentiates between three genres of bodies,57 following a geometrical perspective. Accordingly, the first genre is a body composed of particles arranged in many arm-like parts, which extend as the branches of trees taking diverse directions with many intervals. The second is a body composed of more solid particles presenting globe, cubical, or multiangular figures that stand beneath the first body or mingle with other bodies, occupying its intervals. The third is composed of elongated and branchless bodies, like sticks that intermingle within the first body.58 These particles move and arrange, ultimately composing the diverse bodies of the Earth. The second division (B) concerns the formation of the matter composing the Earth, which traditionally are the four elements, water, air, earth, and fire.59 Following this division, Descartes focused on the nature of these elements and their activities—such as dilatation and condensation for the air (art. 46 and 47), tides for water (art. 49–56), and so on.

4.4.2

The Earth as a Chymical Laboratory

In discussing the nature of earth, Descartes then provided the third division of bodies (C), which is a chymical description of them. In this case, he discusses the nature of minerals and inert bodies growing in the ground, conceiving of the Earth as a great laboratory of chymical bodies. Accordingly, diverse particles of matter, namely salt, air, water, or even subtle matter interact, mix, fill the intervals of other bodies, and are generally moved by the globules of heat.60 Restricted to the physics of extended matter, Descartes leaves no space for alchemical notions such as the anima mundi or seeds and avoids any appeal to substantial forms and other qualities. In the third group of bodies (C), Descartes started by explaining the nature of: 1. quicksilver, which comes from the watery body in the Earth, filtered through the intervals of particles of earth, and whose particles have smooth, rod-like, and polished figures, ultimately composing a heavy and non-transparent liquid body, easily agitated by the globules of fire (art. 58);61

57

Principia philosophiae, III, art. 33, AT VIII-1 220. Cf. Principia philosophiae, III, art. 33, AT VIII-1 220. 59 The interaction of such bodies in the parts of the Earth is a complex segment of the Principia, see Joly 2011: 96–108; and 224–225 (Appendix I). 60 Principia philosophiae, IV, art. 57, AT VIII-1 238–239. 61 Principia philosophiae, IV, art. 58, AT VIII-1 239; MM 211. See further discussion in the correspondence with Elisabeth of Bohemia, and especially in Descartes to Elisabeth, August 1644, AT IV 136–137; and to Cavendish, Descartes to the Marquees of Newcastle, November 23, 1646, AT IV 572. 58

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2. acrid and acid juices, which result from the broken and transformed particles of salt, flattened and repeatedly hammered, and agitated by the force of heat, for these particles undergo a series of deformations moving through the pores of salt, ultimately sharpening and taking a precise figure, before transforming in acrid, acid and corroding juices (art. 61); 3. and an oily matter made by softer, round particles, and being made thin, crushed in these pores, and separated in flexible branches that adhere to other bodies (art. 62). Descartes then points out that these bodies correspond to the three principles of Paracelsian chymists: Quicksilver is alchemist’s mercury, acrid juice is their salt, and oily matter is their sulfur (art. 63). To be precise, however, these bodies do not compose chymical natures or substantial bodies in Descartes’s philosophy, but rather reveal general bodies with a geometrical common structure and mechanical properties, ultimately performing specific activities. For instance, acrid and acid juices corrode other bodies and when thickening with metallic matter, they compose bodies such as vitriol (copper sulfate), or uniting with stony matter, they compose alum, and so on depending on whether they mingle with other materials; while oily matter adheres to bodies, composing coagulates such as sulfur, bitumen, and other fatty and oily bodies. Accordingly, the activities of these three principles (1, 2, and 3) form all mineral bodies in mines. This is anticipated by article 63, where he writes that “acrid juices [. . .] separate some particles of metals. Then, after these particles have become enveloped by and covered with oily matter, they are easily carried upward by quicksilver which has been rarefied by heat; and they form various metals according to their diverse magnitude and figure” (Principia philosophiae, IV, art. 63, AT VIII1 242; MM 213). Moving from this third division of nature in (1) quicksilver, (2) acrid and acid juices, and (3) oily matter, Descartes then described several kinds of metals—but the list lags incomplete because of the lack of experiments.62 First, Descartes described the production of salt from the circulation of water: While entering the earth, water arises attracted by the heat of the Sun, and in being vaporized it loses the particles of salt that sediments and fills the cavity of the Earth (art. 66–68). When salt enters the narrow pores of earth, it changes figures and transmutes into saltpeter or niter and sal-ammoniac (today, ammonium chloride). This variation entirely depends on the different figures of particles composing the body (art. 69). Then, in moving from the division of bodies (C), Descartes specified four kinds of exhalations, as he claims that the movement of these exhalations eases the production of minerals. These exhalations are (i) water vapors, (ii) acre spirits, produced by the rarefaction of corrosive juices and also salt volatile, (iii) quicksilver vapors, and (iv) oily exhalations (art. 70). All of these exhalations move differently within the Principia philosophiae, IV, art. 63, AT VIII-1 242: “quae fortasse singula descripsissem hoc in loco, si varia experimenta, quae ad certam eorum cognitionem requiruntur, facere hactenus licuisset.” 62

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earth, mixing with diverse particles and composing a few minerals. Acre spirits (ii) produce transparent stones, minerals, gems, diamonds, agates, crystals, and other precious stones (art. 71). Quicksilver vapors (iii) carry particles of metals such as gold, silver, and lead, or when coated by the sulfuric exhalations, quicksilver composes cinnabar (mercury sulfur), or also transports several metals such as copper, iron, antimony (art. 72). Joined to the slenderer parts of spirits, oily exhalations (iv) compose branching particles that (1) mingled with metallic particles and acrid juices compose sulfur, (2) mingled with earthly particles and oily juices compose bitumen, naphtha, etc., (3) mingled with earthly particles compose clay, (4) accumulating alone, these particles compose oil (art. 76). An important differentiation surfaces in this list. According to Descartes, metals such as gold, silver, lead, iron, copper, and antimony are simple bodies, composed by the juxtaposition of similar parts with similar figures or shapes63 and carried by juices or exhalations. In contrast, minerals are mixtures composed by the mingling of minerals and juices, exhalations, and so on: “all the substances which are mined are formed by their mingling in various ways” (Principia philosophiae, IV, art. 70, AT VIII-1 245; MM 216).64 As noted by Joly, in differentiating between metals and minerals, the former are simple bodies, while the latter are mixtures, Descartes provided an original interpretation of the seventeenth-century mineralogy. This conception challenges the transmutation of metals, which is only possible if metals are mixtures of different bodies. Yet, Descartes did not pursue this point any further.65 In the following articles, he explains how much these bodies produce earthquakes and fires, as in volcanoes (art. 77–79) and then describes the nature of fire (art. 80). Accordingly, fire is not a new body or a new substance nor belongs to a specific faculty of the burning body, but only depends on the presence of the matter of the first element, whose connection with other particles is removed. While this section is important in the economy of the text, as Descartes is trying to explain the four traditional elements within his mechanical framework, I only focus on its relationship with the study of inert bodies such as metals, stones, and minerals. For example, in describing how fire is kindled by the presence of particles of fire included in bodies, Descartes explains how one can produce fire in stones and in dry wood, two common phenomena discussed in his correspondence (art. 84 and art. 85). For the first case, Descartes reduces this production to the mechanical structure of such a stone, namely flints, which are fairly hard and rigid, and fairly friable. Being hard and rigid entails that, when struck by another body (see flint B in Fig. 4.1), the spaces where globules of the second elements lie (see flint A in Fig. 4.1) become narrower, and these globules are forced out of the space (see flint C in Fig. 4.1), leaving nothing around but the matter of the prime element, namely fire. Then he adds that “as soon as the particles cease to be compressed by the striking, then because flints are rigid 63

Cf. Principia philosophiae, IV, art. 63, AT VIII-1 242. Original Latin is: “atque ex diversis eorum mixturis omnia fossilia componuntur.” 65 Joly 2011: 119–120. 64

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Fig. 4.1 How fire is struck from flints: flint A has globules of air, flint B is struck and particles are removed, as shown in flint C, when fires develop. In René Descartes, Principia philosophiae, IV, art. 84, AT VIII-1 251

[. . .] and because flints are friable [. . .] some of these particles fly apart and, by intermingling with the pure matter of the first element which surrounds them, form a fire” (Principia philosophiae, IV, art. 84, AT VIII-1 251–252; MM 221). Similarly, friction kindles fire in dry wood, as its action shrinks the pores of the body and agitates the particles of the first element; while in other cases, the latter particles mingle with juices and exhalations producing fires (art. 88), or with particles of salt in seawater (art. 91), or in quicklime, in fermentations, in the liquids known by Chymists, and in stored hay. In article 92, Descartes discusses the latter case, as a spontaneous blaze is kindled in stored hay due to the presence of spirits or juices generally flowing through the channels of plants. In drying, the pores of grasses become “too narrow to admit juices and the globules of second element [and] juices are surrounded by the matter of the first element [. . .] acquir[ing] the agitation of fire” (Principia philosophiae, IV, art. 92, AT VIII-1 256; MM 225) and ultimately kindling a fire. Here, Descartes provides a framework to explain vegetal

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fermentation, previously used as a case to describe a few living functions.66 As a result, in reducing the heat within the heart to a chymical activity, namely fermentation, which is a mechanical operation common in diverse bodies, Descartes completes his rejection of traditional innate heat (or vital heat). At the same time, he seems to dismiss all alchemical theory of universal ferment; while he acknowledges the presence of a ferment or yeast, he reduces all fermentation to a mechanical arrangement of particles.67 According to Descartes, the conservation and differentiation of fire depend on the arrangement of particles of bodies to which the fire is connected. The interaction of bodies thus favors different phenomena, such as the increasing of fire by the addition of water to fossil coals or by the addition of salt, which agitates the flames (art. 105). In all these cases, the movement of particles and the presence of air ease the fire, springing violently the first matter out of pores, or only agitating this body. In general, the combustibility of bodies relies on the facility through which particles rearrange or take different shapes, leaving space for the first element of fire. It is to be noted that this rearrangement follows a geometrical pattern according to Descartes. Another issue concerns the case of gunpowder, manufactured from sulfur, niter, and charcoal, which he inspects within a mechanical perspective (art. 109). First, Descartes examines the diverse bodies: “sulfur is by itself as flammable as possible; because it is composed of particles of acrid juices, which are coated by such tiny and dense branches of oily matter that very many pores [. . .] are accessible only by the first element.” To which he adds that, for this mechanical reason, “sulfur is considered extremely hot for medicinal purposes” (Principia philosophiae, IV, art. 109, AT VIII-1 263; MM 232). In contrast, “niter [. . .] is composed of oblong and rigid particles, which however differ from those of common salt” (Principia philosophiae, IV, art 110, AT VIII-1 263–264; MM 232) and whose shape makes it move very fast and increase the fire. Then, after discussing how these two bodies act one on another (art. 111) and how the motion of niter produces a flame that expands exceedingly (art. 112), Descartes describes charcoal (art. 113). Finally, he expounds the force of gunpowder as a suitable arrangement of different bodies: “when fire (which has been brought from elsewhere) first touches the surface of some grain [. . .]. [It] first ignites the sulfur there, the fire gradually also causes violent agitation in the particles of niter; so that, when these particles have finally acquired force, and demand great space [. . .] to describe their circles, they break the bonds of the charcoal and shatter the entire grain” (Principia philosophiae, IV, art. 115, AT VIII-1 265; MM 234). In explaining the mechanics of explosion, Descartes applies his methodology and the knowledge of particular bodies to specific phenomena: What causes the explosive phenomenon is not the mere combination of substances, but there is a more

66 The example of stored hay is also in L’Homme AT XI 121. Primae Cogitationes circa generationem animalium, AT XI 538. Discours de la Méthode, V, AT VI 46. Les Météores, VII, AT VI 322. Other fermentations are in Descartes to Plempius, February 15, 1638, AT I 530–531. Descartes to Cavendish, April 1645, AT IV 189. 67 On fermentation in Descartes’s interpretation of living bodies, see Baldassarri 2021a: 77–97.

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internal reason, relying on the structures of sulfur, niter, and charcoal, and in the movement, shapes, and figures of their particles. Although in this case he appeals to a series of chymical experience with niter and other bodies, he nonetheless reduces this effect to the mechanics of particles. Then, Descartes explains the case of the continuous burning phenomena (art. 116), such as the one related to ignis fatuus [giddy flame], “a tiny and dim light indeed, but one which could easily recover its force from the movement of the external air when the place was opened up and the soot had been dispersed” (Principia philosophiae, IV, art. 116, AT VIII-1 266; MM 235). And then, he discusses a few other phenomena, such as “fire gives off light, [. . .] heats, [. . .] breaks down [dissolvat] all the bodies on which it feeds into many particles [. . .]. However, it remains for us to show briefly how, by the force of fire, certain bodies by which it is not fed become liquid and boil, while others are dried and become hard; [and how] some are given off as exhalations, and some transformed into lime or glass” (Principia philosophiae, IV, art. 117, AT VIII-1 267; MM 235–236). As Joly has pointed out, in collecting diverse effects caused by fire on bodies, Descartes develops a short treatise of distillation. The first case concerns liquefaction and boiling, occurring in bodies with similar or equal parts (art. 118). Descartes specifies that these bodies do not fuel the fire. The second one concerns the solidification of unequal bodies, composed of “slender, flexible, and slippery particles [. . .] not very firmly joined” (Principia philosophiae, IV, art. 119, AT VIII-1 268; MM 236) as in expelling the first, the body loses fluidity and becomes harder (art. 119). The third case concerns evaporation. In this case, Descartes focuses more specifically on several kinds of bodies. He also refers to chymists’ alembics, therefore revealing that he performed a few observations in this case following the chymical experimentation of the period.68 The first group of bodies (a) resulting from evaporation is collected in such sealed flasks, where heated by fire, the slenderest bodies produce “ardent waters, or spirits; such as are usually extracted from wine, wheat, and many other bodies” (Principia philosophiae, IV, art. 120, AT VIII-1 268; MM 237). The second group (b) is made of “sweet or insipid waters, such as those which are distilled from plants [. . .]. Third [(c)], there are the eroding and acid waters, or bitter juices, which are extracted from salt” (Principia philosophiae, IV, art. 120, AT VIII-1 268; MM 237). The fourth group (d) of bodies concerns sublimates that are “bulkier particles (such as those of quicksilver and of salt, which adhere to the tops of alembics and congeal into solid bodies [. . .]” and the fifth (e) oils that “are exhaled by hard and dry bodies” (Principia philosophiae, IV, art. 121, AT VIII-1 269; MM 237). And in the latter cases, Descartes recommends to pour abundant water to extract such bodies. Despite the many references to chymistry and chymical experimentation, Descartes’s list of bodies appears far from a chymical systematization. For instance, each body resulting from distillation has a diverse origin: (a) Spirits result from wine

68 This addition is in the French translation of 1647; Principes de la philosophie, IV, art. 120, AT IX-2 264–265: “comme on experimente fort clairement par la Chymie.”

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or wheat, (b) sweet waters from plants, (c) acid waters or bitter juices derive from salt, (d) sublimate from mercury, (e) oils from dry bodies. In contrast, chymists usually claim that diverse natures could be drawn from the same body, for they conceived of these natures as principles. Descartes rejected the latter claim (as previously seen in his correspondence with Mersenne)69 and conceived of distillation as a universal process that gives different results following a geometrico-mechanical arrangement of particles.70 Chymistry is thus reduced to his mechanical physics. The two last effects of fire are calcination (art. 123) and vitrification (art. 124–132). Descartes discusses these activities, spelling out the various characteristics of glass, before dealing with the last case of this section on inert bodies, the magnet. Undoubtedly, these pages reveal a deep exploration of the nature of particular bodies, especially of minerals and metals, whose knowledge is achieved through experimentation and observations. Descartes interpreted these results in the light of his mechanical physics, ultimately claiming that the diverse properties of bodies belong to their structures and to the arrangement, shape, and figures of terrestrial particles composing them and interacting with globules of air and prime matter, the three elements of Descartes’s physics. Besides the reduction of chymistry to his mechanical physics and the rejection of alchemical principles, Descartes’s study of particular bodies results from observations and experimentation, and it appears clear that the Earth is a great alembic for Descartes—ultimately showing the formation, exhalations, extractions, sublimations, and distillations of diverse matter. Yet, these compositions of mineral bodies are mechanically expounded. Descartes fleshed this out in a response to Elisabeth of Bohemia, who had asked him about the nature of quicksilver.71 Descartes’s reply sheds further light on his physical study of inert bodies. Accordingly: the little particles of air, of water, and of all the other terrestrial bodies have several pores through which the very subtle matter can pass, and this follows well enough from the way in which I have said these particles are formed. Thus, it suffices to say that the particles of quicksilver and of other metals have fewer such pores in order to understand how these metals are heavy. [. . .] each particle of water is like a little cord which is very soft and very loose and that those of quicksilver, having fewer pores, are like other little cords which are much harder and tighter. (Descartes to Elisabeth of Bohemia, August 1644, AT IV 136–137; Shapiro 84–85)

In this letter, Descartes summarizes the points of his mineralogy: in order to understand the nature of quicksilver (and other metals or minerals) one should study the arrangement, shape, and figures of particles (and pores) consistently to his mechanical reduction of nature. In the Principia, he grounds this knowledge on 69

Cf. Descartes to Mersenne July 30, 1640, AT III 130–131. Although Bernard Joly claims that Giambattista Della Porta’s treatise De distillationibus (1608) could operate as source for Descartes, this text presents several differences from the articles of Principia philosophiae. 71 Elisabeth of Bohemia to Descartes, August 1, 1644, AT IV 132; Shapiro 83. 70

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the mechanical principles of his physics (and his metaphysics), ultimately bridging the gap between the principles of his philosophy and the study of particular bodies by means of the history of natural phenomena. Yet, he achieved his science of minerals, metals, salt, and inert bodies by means of chymical experimentation, a necessary tool to make his principles work in the study of particular bodies.

4.5 4.5.1

The Magnet Magnetism Before the Principia

In the same letter of August 1644, Elisabeth of Bohemia raised a second question concerning Descartes’s explanation of magnetism, which composes a relevant section of Part 4 of the Principia, from article 133 to article 186. Before exploring this exchange, let us now focus on magnetism more in detail.72 Since Ancient times, the magnet (or loadstone) has drawn crucial attention due to its power of attracting and repelling iron (and other bodies), and of aligning along a north–south axis. These features posed serious challenges to the Aristotelian elementary qualities and substantial forms. While scholars in the Renaissance tried to propose alternative accounts of magnets, as listed by Christoph Sander,73 the foundation of a geomagnetic theory was laid by William Gilbert’s (1544–1603) De Magnete, Magneticisque corporibus, et de magno magnete tellure (1600). Magnetism and attraction in bodies were not estranged from Descartes’s context. Both Francis Bacon and Galileo had discussed this subject,74 and these were authors whom Descartes knew very well. In the 1631 correspondence with Mersenne, van Helmont speaks of a magnetic force,75 and the same Mersenne explored this issue in his texts. A more important case is Dutch scholar Isaac Beeckman, whose proximity to Descartes is well known. The former proposed a corpuscularian interpretation of magnetism, imagining that tiny particles were emitted from a magnet, traveled through the air, and entered the iron. As Klaas van Berkel has shown, Beeckman influenced contemporary philosophers such as Descartes and Pierre Gassendi in this case.76 In the case of Descartes, there is something more as in August 1644 Johannes Smetius (1590–1651) wrote to Huygens that a few centuriae of Beeckman’s Mathematico-physicarum meditationum, quaestionum, solutionum centuria (1644)

72

Cf. Lüthy 2006. Andrade 2013. Sander Forthcoming. Sander 2022. Cf. Garzoni, Trattati della calamita. Ugaglia 2006. 74 On Bacon, see Jalobeanu 2020. On Galileo, see Reeves 2002. 75 See van Helmont to Mersenne, January 30, 1631, CM III 54, and March 29, 1631, CM III 135. 76 Van Berkel 2013: 7. On Gassendi, see Palmerino 2008. Palmerino 2022. 73

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reveal that Descartes was not the first to propose a corpuscular interpretation of magnetism.77 While it is not my task to investigate the originality of Descartes’s magnetic interpretation in the Principia, the role of Beeckman cannot be underestimated in specifying the context in which Descartes developed his theory. Indeed, Beeckman faced the challenges magnetism posed to a mechanical interpretation of nature, and he considered the phenomenon of attraction in lodestones as the most wonderful matter78 but refused the possibility of an action at a distance, or without any contact. In this sense, Beeckman clearly rejected Gilbert’s theory of an attractive force that was not of a material nature.79 As van Berkel has shown, Beeckman proposed that “a magnet sends out a very fine material, the ‘spiritus’, in all directions. The particles of this material can penetrate the pores of certain bodies, in particular iron. The form of these pores in the iron object corresponds exactly with that of the particles of the spiritus. At those points where the spiritus of a magnet penetrates the interior of an iron object, the pressure of the surrounding air is lifted, while the spiritus particles [. . .] exert no pressure on the iron.”80 Later, Beeckman replaced the air particles with the fire particles or igniculi and claimed the particles of stone have a specific shape. The mechanical problems affecting Beeckman’s interpretation later surface in Descartes’s Principia philosophiae, as I am going to show in a while. Yet, although it is today clear that Descartes’s corpuscular natural philosophy is indebted in many respects to Beeckman’s idea, and magnetism is just an example of this, it is also evident that Descartes produced a more exhaustive theory, different and autonomous from Beeckman’s. In his correspondence with Mersenne, Descartes distances himself from Beeckman’s theory. In a November 1630 letter in which he criticized the boastfulness of a pedant, Descartes also writes about a magnetic experiment to dismiss an explanation of the motion of chords likely set forth by Beeckman. Accordingly, as in the magnetic attraction of iron, Beeckman claims the presence of a medium body,81 in the motion of chords there is a moment of rest in the middle of diverse movements.82 In both cases, the power to move appears to pertain to a middle body, and

J. Smithius to Huygnes, August 12, 1644, in Briefwisseling IV 47: “Magnetica Cartesii tuo nuper beneficio Zutphaniæ legi, seb ab illo tempore Centuriam vidi Meditationum mathematicophysicarum, A° 1628 scriptam, recens hoc anno typis editam, Isaaci Beeckmanni Dordraceni pædagogiarchæ, in quibus, quæ numero 36, 77, 81 et 83 est, ostendit non Cartesio ista corpuscola primum in mentem venisse.” The same passages of the Meditationum are collected in Beeckman’s Journal. English translation of the letter is in van Berkel 2013: 173. It is difficult to understand what Smetius conceives as Descartes’s magnetic philosophy, since the Principia were not published before August 1644; see Verbeek et alii 2003: 75. 78 Cf. Beeckman, Journal, II, 339. 79 Cf. Beeckman, Journal, III, 17–18. 80 Van Berkel 2013: 94–95. See Beeckman, Journal I, 36. Cf. Beeckman, Mathematico-phisicarum: 14. 81 See Beeckman, Journal, II 119; II 387. 82 See D’Agostino 2022. 77

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not to magnets or chords. Neither theory is correct, according to Descartes.83 In contrast, the experiment suggested by Mersenne to Descartes confirms the latter’s theory, according to which the attractive power cannot be interrupted and is therefore internal to the magnet.84 Likely, Mersenne borrowed this experiment from Niccolò Cabeo’s (1586–1650) Philosophia magnetica (1629), a text Descartes had refused to read at that time.85 A month later, he sent Mersenne a magnetized needle and asked him to confirm what the owner of the needle told him about its properties.86 At this stage, however, Descartes’s interpretation of magnetism lacked a theory, and he appeared more interested in discussing the matter as an example for his methodology and epistemology. Indeed, while there is no discussion of magnetism in Le Monde, references to magnets could be detected in earlier works such as the Regulae ad directionem ingenii. Here, the magnet exemplifies a case of the application of his methodology to know complex bodies, whose nature cannot be reduced to an entity known by our intellect.87 In Rule 14, for instance, Descartes claims that one should not construct this knowledge from such an unknown entity, namely magneticity, as this is beyond human understanding (and science); in contrast, one should build from the combination of familiar entities, which are “extension, shape, motion” (Regulae ad directionem ingenii, XIV, AT X 439; CSM I 57). Despite the difficulties, the knowledge of simple natures grounds the study of magnet. In Rule 13, he suggests that one should move from the observations on magnets performed by Gilbert, or to co-opt Gilbert’s lab based on experiments on magnetism, a point brilliantly discussed by John Schuster.88 However, a different program of investigation of magnet is in Rule 12, in a section that is absent in the earlier text of the Regulae, today known as the Manuscript of Cambridge, and likely added by Descartes during the 1630s. In this text, he affirms that: someone who thinks that nothing in the magnet can be known which does not consist of certain self-evident, simple natures: he [. . .] should proceed [in this way:] First he carefully gathers together all the available observations [experimenta] concerning the stone in question; then he tries to deduce from this what sort of mixture of simple natures is necessary for producing all the effects which the magnets is found to have. Once he has discovered this

83 Descartes to Mersenne, November 4, 1630, AT I 172. Descartes to Mersenne, November 25, 1630, AT I 180–181. 84 Descartes to Mersenne, November 4, 1630, AT I 176: “J’estime fort bien l’expérience de l’aimant que vous m’apprenez, et je juge bien qu’elle est véritablee; elle s’accorde entièrement aux raisons de mon Monde, et me servira peut-être pour les confirmer.” 85 Descartes to Mersenne, November 25, 1630, AT I 180; CSMK 29: “I have not seen Cabeus’ book on the Magnetic Philosophy, and at the moment I do not want to be distracted by reading it.” On Cabeo, see Martin 2006. Waddell 2015. 86 Descartes to Mersenne, December 2, 1630, AT I 191: “Je vous envoie une aiguille frottée d’une pierre d’aimant qui pèse environ deux livres, et qui en lève jusqu’à vingt étant armée; mais désarmée, elle n’en lève pas plus d’une. Il décline de cinq degrés, à ce qu’on m’a dit; mais je n’en suis pas fort assuré; car celui qui l’a, n’est pas fort intelligent. Je ne sais si c’est la même pierre que vous avez vue, mais on m’a dit qu’il n’y en avait point de meilleure en cette ville.” 87 See Shea 1991. 88 See Schuster 2013: 558–561. Cf. Regulae ad directionem ingenii, XIII, AT X 431; CSM I 52.

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mixture, he is in a position to make the bold claim that he has grasped the true knowledge of the magnet. (Regulae ad directionem ingenii, XII, AT X 427; CSM I 49–50)

This passage is meaningful, for Descartes claimed that one could achieve the knowledge of simple natures, namely the intelligible entities, of magnetism, by deducing them from observations. This is a posteriori knowledge, moving from the effects back to the causes by the help of observations—this epistemology characterizes Cartesian mineralogy by large, as noted in this chapter. Accordingly, by gathering all the effects produced by magnets, one could deduce its composition, and in which ways the extension, arrangement, shape, figures, and movement of its particles produce its phenomena. At this stage, Descartes stressed that both observations and composition are the first moment in the path of knowledge, revealing the efficacy of the method in constructing knowledge from experimentation. It also entails that any study of particular bodies mostly develops from observations and experimentation. However, no explanation of magnetism surfaces in the early 1630s. Still, this claim appears significant, as Descartes later engaged with magnetism by gathering diverse observations. In December 1639, he comments on “a few observations on the magnet” (Descartes to Mersenne, December 25, 1639, AT II 636) that Mersenne shared with him (and also with Grotius, Haack, and other scholars).89 Later, in discussing an English book on the declinations of the magnet, Descartes states that “no credit could be given to this text, as [he] would not do 3, but 1000 observations before being sure [on this matter], as a little thing may change their results” (Descartes to Mersenne, January 29, 1640, AT III 7 [translation is mine]).90 In the same letter, he claims to “know since long time about the observations on magnets you write me, and I easily can explain them in my Monde, but pretend to explain the whole physics through the magnet is quirk” (Descartes to Mersenne, January 29, 1640, AT III 7 [translation is mine]).91 What is important to note is that Descartes rejected the reduction of physics to magnetism, as either Gilbert or Daniel Chorez did,92 therefore confirming his epistemological claim that the knowledge of nature could not be inferred from obscure objects—such as the lodestone—but works the other way around, from familiar entities—such as extended matter—to unknown objects.93 Descartes’s correspondence of these years follows a twofold path. Together with his rebuking of curiosities, fables, superstitions, or false experiments and opinions

89

Cf. CM VIII, 754–762 (Appendix 2); CM VIII 482, 533, 584. The book in question likely is H. Gellibrand, A Discourse Mathematical on the Variation of the Magneticall Needle. See Pell to Descartes, November 21, 1639, in CM VIII 631; see also Mersenne to Kircher, January 20, 1640, CM IX 32–38; Mersenne to Haack, February 25, 1640, CM IX 134–138. 91 Original French is: “J’ai su, il y a longtemps, toutes les Expériences de l’Aimant dont vous m’écrivez, et puis aisément donner raison de toutes dans mon Monde; mais je tiens que c’est une extravagance de vouloir expliquer toute la Physique par l’Aimant.” 92 On Chorez, see Descartes to Mersenne, March 11, 1640, AT III 42. 93 Cf. Regulae ad directionem ingenii, IX, AT X 402. Cf. Galison 1984. 90

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concerning the magnet in the epistolary exchange with Mersenne,94 as scholar’s speculations appeared dangerous and useless to him, Descartes’s own interpretation of magnetism slowly surfaced. In January 1643, Descartes commented on Jesuit Athanasius Kircher’s (1602–1680) Magnes sive de arte magnetica (1641) with Huygens.95 And in May 1643, he spelled out his explanation of magnetism, which anticipates the content of the articles of the Principia. This is the text: I explain all the properties of magnetism by means of a very subtle and imperceptible kind of matter which emerges continuously from the earth, not just from the pole, but from every part of the Northern hemisphere, and then passes to the south, where it proceeds to enter every part of the Southern hemisphere. There is a corresponding kind of matter which emerges from the Earth in the Southern hemisphere and re-enters the Earth in the north. Now the particles of these two kinds of matter are shaped in such a way that they cannot easily pass through the gaps of air or water or several other kinds of body; moreover, the pores of earth and of magnetite which allow passage to the particles coming from one hemisphere cannot be entered by those from the other hemisphere. I think I demonstrate all this in my Physics, where I explain the origin of those kinds of subtle matter, and the shapes of their particles, which are long and spiralling like a screw—the northern ones twisting in the opposite direction to the southern ones. Now, what causes the declination of needles when they are parallel to the horizon is that the subtle matter that allows them to move comes from distant parts of the Earth on an unequal surface. This inequality entails that the subtle matter does not abundantly come from the Pole as from the places that decline from it. This cause partially stops when needles are perpendicular to the horizon, because at this moment subtle matter, coming out from the places where needles are, sets them upright. Still, since more subtle matter coming from the opposite Pole helps to set them upright, I believe these should decline less than the other, and not that these do not decline at all; and I would be happy to see by an observation if my conjecture is correct. As for the reason that makes these perpendicular needles to turn on the same side, I explain it like Father Mersenne does, as I belief this depends on the fact that iron has a latitude and that subtle matter entering it does not arise completely straight from the bottom to the top, but takes its own course declining a bit, in this Boreal hemisphere towards the Austral [hemisphere]. For example, if the needle is ACBD [see Fig. 4.2], subtle matter coming from the earth forms in it pores that lean from B towards A. And steel is of such nature that its pores could be arranged in that way, when touched by a magnet, as there is a lot of subtle matter around the magnet, and the pores of steel maintain their arrangement, once they receive it. (Descartes to Huygens, May 24, 1643, AT III 816–818. CSMK 220 [translation is for 816, the rest is my translation])

The matter of discussion is the magnetic experiment of the Jesuit Jacques Grandamy (1588–1672) on a compass without variation, a spherical loadstone which he claimed to prove the Earth’s rest.96 In the letter to Huygens, Descartes dismissed Grandamy’s claim and conjectured that the compass should decline, even 94

See Descartes to Mersenne, March 11, 1640, AT III 42; April 1, 1640, T III 46; August 6, 1640, AT III 146; August 30, 1640, AT III 163; January 21, 1640, AT III 285; May 30, 1643, AT III 673. See also Huygens to Descartes, January 25, 1642, AT III 778; January 31, 1642, AT III 781; June 26, 1643, AT III 824. 95 Cf. Descartes to Huygens, January 14, 1643, AT III 803–804. See Excerpta ex P. Kircher De Magnete, AT XI 635–639. On Kircher, see Rowland 2000. Stolzenberg 2001. Findlen 2004. Fletcher 2011. 96 See Verbeek et alii 2003: 78, n. a.

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Fig. 4.2 The needle ACBD, with the pores directed from B to A, in Descartes to Huygens, May 24, 1643, AT III 817

for a little, something he would confirm late in June against the “false opinion of that Jesuit, who imagined it without proving it” (Descartes to Huygens, June 26, 1643, AT III 824). Descartes’s appeal to experimentation to confirm a theory cannot be overstated. More importantly, this letter contains Descartes’s first reference to screw-shaped particles emitted by the loadstone and by the Earth—that he considers a loadstone in itself. He claims that these particles have a left-handed screw or a right-handed screw according to the Pole they come from and move from one part of the Earth to another—a few days later, in a letter to Mersenne on Grandamy’s experience, Descartes suggests that these particles go “from the Poles toward the Equator and from the center [of the Earth] to the circumference” (Descartes to Mersenne, May 30, 1643, AT III 673). What causes the non-variation experienced by Grandamy is both the distance of the compass from the Poles and the inequality on the Earth, which make such a subtle matter screw shaped little affect the compass. Finally, he declares that needles always move toward the same point, as the movement of screwshaped particles within the body arrange its pores in a specific way toward a specific direction. As it is clear from this letter, Descartes’s mechanical physics—i.e., arrangement and movement—ground the explanation of magnetism. Accordingly, the agents of magnetic attraction are the screw-shaped particles—that he conceives to be similar to shells. These particles enter the threads of the same shape in magnetic bodies, and their movement and contact produce the magnetic force. Magnetism depends on the contact between particles, dismissing any recourse to occult forces. Moreover, following their shape, as these particles are either left-handed or right-handed, Descartes explains magnetic polarity. Furthermore, Descartes considers magnetism

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a cosmic force,97 providing a cosmological reconstruction of the universe. This letter anticipates the explanation of the Principia.98

4.5.2

Screw-Shaped Particles in Descartes

In article 133 of the fourth Part of the Principia, Descartes starts his explanation of magnetism by claiming that this “force is spread throughout this whole globe of the Earth, whose entire bulk is in fact a magnet,” and in order to understand it one should “recall to mind those screw-shaped particles of the first element, which were quite carefully described above in Article 87 of Part III” (Principia philosophiae, IV, art. 133, AT VIII-1 275; MM 243). Indeed, in describing the movement of particles in the universe, Descartes shows that some particles move within the little space between globes, and these “scrapings less divided [. . .] and less rapidly agitated” (Principia philosophiae, III, art. 88, AT VIII-1 144; MM 133) compose particles of matter of the first element “which is moved in straight lines from the poles of each heaven toward its center” (Principia philosophiae, III, art. 89, AT VIII-1 144; MM 133). Since these particles pass through the triangular space between globes, they are “triangular in cross-section” (Principia philosophiae, III, art. 90, AT VIII-1 144; MM 133), and Descartes defines them as screw-shaped particles, or striatae in Latin. In these articles of Part III, Descartes reveals the mechanic-geometrical formation of such particles in detail. According to Descartes, one should: conceive of them as small {fluted} cylinders with three grooves [striis] {or channels} which are twisted like the shell of a snail. This enables them to pass in a twisting motion through the little spaces which have the form of the curvilinear triangle [. . .] and which are always found between three contiguous globes of the second element. For, since these {grooved particles} are oblong and pass very rapidly between the particles of the second element [. . .], these grooves [strias] of each one must be twisted like those in a snail’s shell; and that these are more or less twisted according to the distance which separates the spaces through which they are passing from that axis. . . (Principia philosophiae, III, art. 90, AT VIII-1 145; MM 134)

In sum, screw-shaped particles are formed by passing through the little space between three globes of the second element; as they move, particles take a specific form similar to the shell of snails. Differences in these particles belong to the movement of those globes, which varies depending on their distance from the axis of the vortex. Moreover, since they move from different poles and in different hemispheres, “particles approach the center of the heaven from opposite directions [. . .], while the whole vortex rotates in one direction on its axis, [. . .] and those coming from the South pole must be twisted in exactly the opposite direction from those coming from

97 98

On magnetism in the Universe, see Schuster 2013: 560–561. On the role of magnetism in teaching Cartesian philosophy, see Sander 2023.

4.5

The Magnet

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Fig. 4.3 On the left, the globules within which particles enter and take a screw-shaped form; on the right, screw-shaped particles. In Henricus Regius, Fundamenta physices, chap. II, 53

the North” (Principia philosophiae, III, art. 91, AT VIII-1 145; MM 134). Showing a mechanical difference in the shape of particles according to their position in relationship to the axis helps specify the different powers of magnetism in the two hemispheres, disclosing the conditions of magnetic force on Earth. In article 94 of Part III, Descartes affirms that these screw-shaped particles form the spots usually observed on the surface of the Sun and on other stars, as one could observe in a pot of boiled water. Accordingly, “the matter of the Sun [. . .] must reject like a scum the grooved [or screw-shaped] particles” (Principia philosophiae, III, art. 94, AT VIII-1 148; MM 136). Among several other phenomena one observes in the universe, which are related to the movement of such a spot and the presence of such particles, Descartes also includes the formation of planets such as the Earth.99 For this reason, planets have a magnetic condition, and screw-shaped particles move around them. This cosmological framework is the point of departure for Descartes’s explanation of magnetism. It should be noted that a very similar explanation of such screw-shaped particles (as well as their representation, see Fig. 4.3) is in Fundamenta physices by Regius, who described their formation in a mechanical way consistent with Cartesian philosophy and located them in solar spots, as Descartes did.100 Regius dealt with the terrestrial globe and with the bodies in it, and then with the loadstone that he considered formed by screw-shaped particles: “these screw-shaped matters [. . .] perform all magnetic actions” (Regius, Fundamenta physices: chap. III,

99

Principia philosophiae, III, art. 119, AT VIII-1 168. Cf. Regius, Fundamenta physices: chap. II, 53: “per interstitia globulorum aethereorum, perpetuo circum axem sui vortices circumrotatorum, triangulaira 1 & 2 ex oppositis polis versus centrum transeundo, ex parte, dum quaedam ejus minutiae ramosae vel angulosae inter se conjunguntur, in particular striatas, contrariis sibi mutuo modis contortas 3 & 4 abit.” Regius, Fundamenta physices: chap. II, 65: “Hae originem ducunt à striatis primi elementi particulis . . .”; 66: “Tarditas motus istarum macularum Soli adeo vicinarum, oritur ex eo quod aether, è materia striata ex Sole perpetua ejecta...” On Descartes and Regius on magnetism, see Sander Forthcoming. 100

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79 [translation is mine])101 Even the description of the movement of these particles within and outside the Earth is utterly Cartesian.102

4.5.3

The Magnet in the Principia

Let us now move to the Part 4 of the Principia. In article 133, Descartes stresses that: there are many pores in the Earth's intermediate region which are parallel to its axis, and through which the grooved [or screw-shaped] particles coming from one pole freely proceed to the other. And these pores have been hollowed out to the measurement of these particles in such a way that those which accept the grooved particles coming from the South pole can in no way admit those which come from the North pole; conversely, those which accept the Northern particles do not admit the Southern ones: because of course these particles are twisted like the thread of a screw; some in one direction and the others in the opposite direction. Furthermore, the same particles can enter through only one end of these pores, and cannot return through the opposite one because of certain extremely tiny extremities of branches in the windings of these pores, which have been bent in that direction in which the grooved particles are accustomed to pass, and which spring back in the opposite direction in such a way as to prevent their return. As a result, after these grooved particles have traversed the whole intermediate Earth from one hemisphere to the other along straight lines, or lines equivalent to straight, parallel to its axis, they return through the surrounding aether to that same hemisphere through which they earlier entered the Earth; and thus flowing through the Earth again, form a kind of vortex. (Principia philosophiae, IV, art. 133, AT VIII-1 275–276; MM 243)

In article 146, Descartes explains the movement of these particles through the pores of the Earth by means of a figure (see Fig. 4.4). Particles enter and exit from the Earth, flowing out of each pole and, insofar as they are differently twisted, they move in circle around the Earth and then return to their original pole following different path depending on their shape. While flowing through the Earth, these particles leave some vestiges of their movement “in the bulkier particles [composing] the interior crust of the Earth” (Principia philosophiae, IV, art. 134, AT VIII-1 276; MM 244), therefore shaping the pores of a few bodies within the Earth in a way that suitably ease the movement of such grooved particles. By means of their movement, these particles leave some residues that adhere to the bulkier particles, therefore imparting these latter with magnetic properties. This element is iron, which is made “of particles which are branching and bulky but not very solid, [and] cannot lack these pores” (Principia philosophiae, IV, art. 135, AT VIII-1 277; MM 244). Accordingly, since iron contains more pores than other metals, it easily accommodates screwshaped particles, acquiring magnetic properties. This is confirmed by the fact that iron is harder and less fusible than other metals, while it is also “the least heavy, and

101 Original Latin is: “Ope hujus materiae striatae [...] fiunt omnes actiones magneticae, de quibus postea in ferro & magnete acturi sumus. . .” 102 Cf. Regius, Fundamenta physices: chap. III, 78. See Fig. 4.3.

4.5

The Magnet

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Fig. 4.4 The flowing of screw-shaped particles in the Earth and around it. In Principia, AT VIII1 288

is easily damaged by rust or eroded by aqua fortis” (Principia philosophiae, IV, art. 136, AT VIII-1 278; MM 245). After discussing the movement of screw-shaped particles that specifies magnetism and reveals the magnetic properties of the Earth, Descartes presents the nature of the magnet in article 139. When these particles combine and accumulate, they form “a lump of iron,” while in other cases, those particles that have remained immobile “after having been firmly driven into the pores of a rock or other body, form a magnet” (Principia philosophiae, IV, art. 139, AT VIII-1 279; MM 246). Apparently, for Descartes the loadstone is a fixed iron in the rock, as the lump of iron is similar to the magnet, and magnets always contain some iron. Later in the text, Descartes claims that “the magnet is burdened with much stony matter” (Principia philosophiae, IV, art. 171, AT VIII-1 302; MM 265).103 Yet, in the French edition of the Principia, Descartes specifies the difference between iron and loadstone: While the particles of matter suitable to welcome screw-shaped particles compose both bodies, the difference relies in the fact that the particles of iron have frequently changed position, but the particles composing magnets have a more fixed position.

103

Cf. art. 172, AT VIII-1 303; MM 266.

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In the following articles, Descartes describes liquefaction as a way to convert iron into steel (art. 140), the quality of steel, which is hard, rigid, and brittle (art. 141), the differences between iron and steel (art. 142), and how one could temper steel (art. 143). After this exploration of such bodies, Descartes is able to flesh out how to differentiate between iron, steel, and loadstone, as all of them have similar pores suited to admitting screw-shaped particles. As noted earlier, the difference belongs to the mechanical structure of these bodies: First, in such bodies, pores could be easily bent, but difficulty returns to their original position; second, the diverse arrangement of such pores in iron and steel makes difficult to screw-shaped particles to enter these bodies. Both reasons depend on the formation of these bodies, which are composed of a combination of different material and grooved particles, and the action of fire makes their arrangement vary, and pores are not all arranged in the same direction. Finally, in iron and steel, pores fail to match the number of screw-shaped particles, as these bodies are composed of diverse material.104 Descartes reduces all these differentiation to the mechanical structure of such bodies: If compared to iron and steel, the magnet has a more precise, fixed, and ordered arrangement of pores, it has more pores suited to admitting screw-shaped particles, and liquefaction or hammering does not affect its structure. In sum, magnetism depends on the movement of screw-shaped particles whose formation has been investigated in the cosmological section of the Principia. While these particles move within the Earth—a great magnet—they leave a trace in the metallic matter, especially in iron bodies, which acquire a few grooved pores. In some cases, such a metallic matter composes pieces of iron (that become steel when labored), while in other cases, namely when particles are more fixed, it composes loadstones. In welcoming screw-shaped particles through their pores, these bodies perform the observed magnetic responses. These phenomena entirely depend on the motion of particles and on the structure of natural bodies; for instance, the arrangement and situation of pores is a meaningful difference between iron, steel, and loadstones, as these bodies behave differently. Descartes not only grounded his explanation on the principles of extended matter but also felt compelled to explain the cosmological origins of screw-shaped particles and the telluric origins of loadstones (iron and steel), therefore describing the causes of magnetism. In article 145, Descartes lists 34 properties of magnetic power, which are discussed from article 146 to 186. This collection of problems written in a questionand-answer format parallels a section of pseudo-Aristotle’s Problemata and has a different structure from Descartes’s synthetic explanation of the Principia philosophiae. I am not going into these articles in detail. It should be noted, however, that the list of article 145 matches the list of magnetic properties Mersenne sent to Descartes in 1639, a list likely drawn from Gilbert’s text.105 Descartes himself refers

104 105

Principia philosophiae, IV, art. 144, AT VIII-1 283; MM 249. See Correspondance de Mersenne, VIII, Appendix 2, 754–762.

4.6

Conclusion

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directly to Gilbert in article 166 concerning the reasons why magnetic force is weaker in the Earth than in a small magnet, and in article 168 on declination.106 In article 171, Descartes affirms that there is no attraction between iron and the magnet because the magnetic force only consists in the motion of screw-shaped particles that “expel[s] the air between the two bodies: as a result, the two approach each other in the same way as two magnets do” (Principia philosophiae, IV, art. 171, AT VIII-1 302; MM 265). In reducing attraction to the movement of particles and mechanical structure of bodies, Descartes completes his study of inert bodies by reducing all phenomena to the principles of his physics and to the movement, shape, arrangement, position, and figures of particles. Descartes repeats this claim in article 187, as “from principles [such as] the figure, magnitude, situation, and motion of particles of matter,” everyone “will be easily persuaded that there are, in rock or plants, no forces so secret, no marvels of sympathy or antipathy so astounding, and finally, no effects in all nature which are properly attributed to purely physical causes or causes lacking in mind and thought.” And everyone will be able to know the nature of rocks, stones, minerals, metals, and magnets as he achieved it in the Principia, namely from the geometrico-mechanical principles of his physics. The conclusion is that “it is unnecessary to add anything else to them” (Principia philosophiae, IV, art. 187, AT VIII-1 314–315; MM 275).

4.6

Conclusion

At the end of the Principia, Descartes stresses that from the knowledge of principles (“which is imparted to our minds by nature” [Principia philosophiae, IV, art. 203, AT VIII-1 326; MM 285]), he could infer the sizes, figures, and arrangements of particles composing diverse bodies and different phenomena—therefore making his explanation of rocks, stones, minerals, metals, and magnets consistent with and reliant to his mechanical physics. Although this downplays the autonomy of chymistry, for his mineralogy works out of his physics, this is a sound achievement of his philosophical program. In the last article of Part 2 of the Principia, Descartes has claimed that “all Natural Phenomena can be explained” from the investigations of “divisions, shapes, and movements [of particles],” whose knowledge develops from the mechanical principles of physics and ultimately lies in the mind “as a Mathematical demonstration” (Principia philosophiae, II, art. 64, AT VIII-1 79; MM 77). This is what he did in Part 4 of the Principia, where the explanation of minerals suitably results from the mechanical reduction of nature to extended matter, and from the laws of motion (which he first applies to cosmology). If Huygens was correct in claiming that in Descartes’s Principia one could discover “the anatomy of things” (Huygens to

106 Cf. Principia philosophiae, IV, art. 166, AT VIII-1 300; MM 262; art. 168, AT VIII-1 300; MM 263.

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Descartes, July 7, 1645, AT IV 779), this knowledge is connected to the principles of his physics, ultimately bridging the gap between his metaphysics and natural philosophy. In this chapter, I have dealt with this gap. First, I have discussed Descartes’s dismissal of the principles of alchemy, while he praised chymical experimentation as a noteworthy tool to study minerals and metals—when encompassed within the principles of his physics. Then, I have disclosed Descartes’s chymical studies, namely his engagement with particular bodies by means of observations, as he dealt with curious bodies. However, in his 1630s correspondence, as well as in the first chapters of Le Monde and in Les Météores, Descartes moved from observations and sensory experience, inferring the principles of chymistry a posteriori—in particular, the case of the Bologna stone reveals Descartes’s impossibility to infer the knowledge of this phenomenon from the principles of his physics, as he needed to observe the stone. Yet, things change in the Principia. In the latter text, experimentation and observations are grounded in the mechanical principles of physics and in metaphysics, therefore providing a less fragmented philosophy. In Sect. 4.2, I have disclosed Descartes’s attempts to deal with particular and strange phenomena. In Sect. 4.3, I have discussed Descartes’s description of qualities in Le Monde, grounded on his observations performed in the early 1630s, as he used these observations to pave the way to his definition of nature as extended matter. Yet, Descartes failed to move from this definition of nature to the exploration of particular bodies, revealing a crucial gap in his early physics. A similar condition surfaces in Les Météores, whose important explanation of the nature of salt is grounded on hypotheses, as he moved from a posteriori knowledge back to causes. In all these cases, Descartes started from observations and experimentation with bodies, reducing their qualities to the sizes, arrangements, and figures of particles composing them, but failing to provide the principles of his philosophy. The study of salt thus emerges as a paradigmatic case to understand Descartes’s mineralogy, as well as his entire philosophy of nature. Finally, in Sects. 4.4 and 4.5, I have disclosed Descartes’s examination of minerals, metals, and magnet in the Principia. Although this explanation produces a short history of natural phenomena, Descartes grounded it on his metaphysical physics, on the mathematical application of these principles to cosmology, and to the formation of the Earth. Moving from a universal history of the formation of minerals and stones, Descartes thus examined the mechanical movements and arrangements of particles producing the diverse bodies, combining his physics a priori with the observation of particular bodies. In sum, Descartes engaged with mineral nature in its entirety, ultimately constructing a science consistent with and pursuant from the geometrico-mechanical principles of his philosophy.

Chapter 5

Plants

Abstract The study of plants is problematic in Descartes’s philosophy, as he failed to include a section on vegetation in his Principia philosophiae and rarely wrote about plants in their own right. When he did, problems surfaced: for instance, his definition of plants fluctuated between nonliving and living bodies. Furthermore, Descartes’s interest in plants did not match the widespread enthusiasm for botanical varieties of his contemporaries, but he mostly focused on the internal functioning of vegetal bodies—something that was not entirely uncommon in the Dutch Republic. In this chapter, after discussing Descartes’s fluctuating definition of plants, I investigate several possible collaborations with his Dutch peers, in order to situate Descartes’s botanical study in its context, and I finally disclose his mechanization of plant life, as he reduced plant generation, growth, and fructification to the geometrico-mechanical principles of his physics. A sound natural philosophical section on plants thus consists of studying vegetating as a mechanical activity internal to living bodies, ultimately uncovering a mechanical differentiation between plants and minerals.

In article 188 of the Principia philosophiae, Descartes notoriously states that the section on plants (which runs together with animals) has not been added to the whole text due to a lack of time in examining these subjects and to the fact that he was “not yet completely clear about all the matters which [he] would like to deal with there” (Principia philosophiae IV, art. 188, AT VIII-1315; CSM I 279). In 1647, he wrote in the Lettre-Préface to the French translation of the Principia that to bring his project to completion with a study of the nature of plants, he needed a number of “observations to back up and justify [his] arguments” (Lettre-Préface, AT IX-2 17; CSM I 188). Yet to what extent he had developed the study of plants raises questions. Certainly, Descartes did not follow the traditional methodology of botanical studies. In the Utrecht crisis, Gisbertus Voetius (1589–1676) and Martin Schook (1614–1669) challenged Henricus Regius’s competence in botany and claimed that Descartes and Regius naively rejected the use of catalogs and incorrectly grounded “a new botanical philosophy [. . .] on the first law of Descartes’s [methodology]” (Schook, Admiranda Methodus: 199 and 233–237). Indeed, although the harbors of © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 F. Baldassarri, René Descartes’s Natural Philosophy and Particular Bodies, Studies in History and Philosophy of Science 60, https://doi.org/10.1007/978-3-031-48663-0_5

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the Dutch Republic gathered all the diverse products of the East and West Indies, and included the strangest vegetal species, which one may collect with ease, “knowing all the herbs and stones coming from the Indies” (La Recherche de la vérité, AT X 503 [translation is mine]) appeared as a massive undertaking that escapes the aims of Descartes’s philosophy. What is more: Besides the references to plants (ivy and tree in the Discours), fruit (a melon or an apple in his 1619 dream),1 gardens, and a few uses of simples for a therapeutic that is only sketched in his biomedical manuscripts,2 a clearer involvement with the science of plants, if not even a botanical philosophy as suggested by Voetius and Schoock, seems to elude Descartes’s philosophical program. Stephen Gaukroger has significantly noted that “unfortunately, we have no record of his work on botany, and it is unclear how far his interest extended” (Gaukroger 1995: 405).3 Several problems characterize this study. The first is whether or not Descartes was involved in the study of plants. Given his rejection of natural histories, collecting, or cataloging efforts and his lack of interest in outward differences, varieties, or naturalistic details that characterized early modern botany, his approach to vegetation would have been far removed from the trends of his time.4 The second is what matter should be treated in a section on plants consistent with his geometricomechanical philosophy. As some attention to plants surfaces in his texts, these reveal how much he aimed to describe vegetal activities and explore the vegetal world to investigate the processes of living nature. Within his physics, he conceived plants as hydraulic machines, and a section on plants should thus disclose the similarities between plants and machines.5 This leads to another issue: Are plants nonliving bodies like rocks and minerals (or mere machines)? Or, do plants testify to any difference between nonliving and living beings in Cartesian philosophy? Two cases possibly illustrate Descartes’s attention to plants. In a July 1633 letter, Mersenne informed Descartes about a clock driven by a Sunflower seed, probably referring to the botanical clock allegedly devised by Athanasius Kircher (1602–1680) (see Fig. 5.1).6 Descartes considered this experience curious and asked Mersenne for more details.7 Still, rather than focusing on the nature of the Sunflower or the relation between magnets and plants, two fascinating issues of seventeenth-century naturalistic knowledge, he appeared more attracted by the

1

Cf. Gabbey 1998; Gómez 2020. See Descartes, Remedia et vires medicamentorum, AT XI 641–644. Cf. Shapin 2000: 149, and Baldassarri 2018a. 3 Cf. Rodis-Lewis 1995. Gaukroger 2002: 186–189. Clarke 2006. 4 See Ogilvie 2006, Ch. 5. Egmond 2017a, Ch. 2–3. 5 Such a comparison is in the Principia philosophiae, IV, art. 203, AT VIII-1326; MM 285–286: “it is as natural for a clock, composed of wheels [. . .] to indicate the hours, as for a tree, grown from a certain kind of seed, to produce the corresponding fruit.” 6 See Vermeir 2013. Čermáková 2018. 7 Descartes to Mersenne, July 22, 1633, AT I 268. 2

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Fig. 5.1 Heliotropic clock. In Athanasius Kircher, Magnes sive de arte magnetica, Rome 1654, 508

Fig. 5.2 The formation of fires in stored hay. In René Descartes, Principia philosophiae, IV, art. 92, AT VIII 256

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mechanical cause of this motion.8 The second example is in the Principia, where Descartes describes the phenomenon of natural fire that ferments in stored hay (see Fig. 5.2).9 This effect, he posited, depends on the movement of spirits and juices within the pores of mown grasses. While he provided a general description of the internal structures of herbs and plants, in this text, he appears more interested in the natural phenomenon of fire occurring in nonliving bodies, and very little in the heating processes in living plants—or living bodies in general. These two examples restrict Descartes’s interest in plants to mechanical features unrelated to vegetation per se, therefore marking a significant disregard of botanical knowledge altogether. Still, in item E of the Inventory of Stockholm, there is a reference to “sixteenth pages [including] observations on the nature of plants and animals” (Stockholm inventory, AT XI 9),10 which testify to more consistent work on plants. Some of this work is today collected in one of Descartes’s biomedical manuscripts, Excerpta anatomica, containing several notes on the physiology of plants. In this chapter, I aim to provide a response to Gaukroger’s claim, disclosing how much Descartes worked on plants and how far his interest in the vegetal world extended, and I aim to answer the questions raised earlier. Grounded on the notes collected in his biomedical manuscripts, Descartes’s involvement with plants appears a more consistent contribution to a natural philosophical understanding of vegetation and makes plants a more significant subject of his program, if not even central in the divide between nonliving and living bodies. In section one of this chapter, I deal with the question of classifying plants, that is, to position plants within a mechanical system. In the second section, I investigate Descartes’s exchanges of botanical knowledge regarding the circulation of specimens and botanical collaborations he had with his peers in order to perform observations to boost his study of vegetation. Finally, in section three, I present his observations of plants, which disclose a scientific knowledge of the internal structure and functioning of plants that led to a mechanization of green nature consistent with Descartes’s natural philosophy, especially with his physiology of living bodies.

8

Descartes had also tried to plant one sunflower, but failed, as he wrote to Huygens in 1643; see Descartes to Huygens 1643, AT III 804. 9 Principia, IV, art. 92, AT VIII-1256. According to Gaukorger, this exemplifies a similitude between sap and blood, but Descartes does not refer to it; cf. Gaukroger 2002: 187. See Chap. 4 on fire and natural bodies. 10 Original French is: “prenant ledit registre de l’autre côté, il y a seize pages d’observations sur la nature des plantes et des animaux.”

5.1

Classifying Plants

5.1 5.1.1

121

Classifying Plants Plants and Animals: Mechanical Analogies and the Vegetative Power

In his major works, Descartes rarely spoke of plants. In Discours de la Méthode, he claimed that plants were a subject of his unpublished treatise on physics—Le Monde—where he had been working on how “mountains, seas, springs and rivers could be formed naturally [on the earth]” and “how metals could appear in mines, plants grow in fields, and generally how all the bodies we call ‘mixed’ or ‘composite’ could come into being there” (Dscours de la Méthode, V, AT VI 44; CSM I 133). As I have shown earlier, such a study of particular bodies is, however, missing. Yet, something else surfaces. A page later in the Discours, Descartes repeated that in his physics he moved “from the description of inanimate bodies and plants [. . .] to describe animals, and in particular men” (Dscours de la Méthode, V, AT 45; CSM I 134). While no references to plants surface in Le Monde,11 bracketing plants together with inert bodies appears problematic. This definition possibly depends on the fact that both rocks and plants are fastened to the ground: as metals grow in mines and plants adhere to the soil and grow from the earth.12 In both cases, growing from the earth entails that in plants the nutrients enter from outside, similarly to what occurs in rocks, minerals, and metals. Possibly, this is the paradigm Descartes followed to organize bodies in his natural philosophy at this stage, which also entails that he approached the vegetation of plants as a process similar to those occurring in inert bodies and different from those of animals. As is well known, Descartes rejected Aristotelian tradition and the natural philosophical interpretations Aristotelians propose for plants. According to the latter, what makes a plant a plant is the vegetative soul, namely a psychological principle for vegetating. Consistent with this point, Aristotelian philosophers generally started their sections on plants by defining the vegetative soul as the principle activating vegetal functions and helping specify their nature.13 In the late sixteenth century, scholars such as Giovanni Costeo (1528–1603) and Franz Tidike (1554–1617), in De Universali stirpium natura libri duo (1578) and Phytologia generalis (1582), respectively, introduced a study of plants with a discussion of the vegetative soul. In De plantis libri XVI (1583), Andrea Cesalpino (1524/1525–1603) provided a systematization of plants by means of the functions of the Aristotelian vegetative soul.14 Some decades later, the French philosopher Guillaume Du Val (?1572–1646) 11 In Le Monde, Descartes mentions plants just in one case, as he stresses that “plants and animals are always either growing or decaying” (Le Monde III, AT XI 11; G 9), but this definition appears more general than the one in the Discours, where he specifies what makes him gather plants together with metals. Since all bodies grow or decay, this does not deny the division of the Discours. 12 This point has been recently raised by Daniel Garber. See Garber 2022. 13 On the vegetative soul in philosophical traditions, see Baldassarri and Blank 2021. 14 See Baldassarri 2023b.

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discussed the vegetative soul at large in Phytologia, sive philosophia plantarum (1647), conceiving it as a crucial benchmark for defining vegetation.15 Descartes challenged this framework, as souls fail to explain living activities and are unsuited to differentiate living from nonliving bodies, or to construct a scale between beings.16 In contrast, he claimed that the mechanical arrangement of particles helps explain the functions and processes of all bodies and reveals the organization of and identity between bodies.17 The same mechanical principles and the same mechanical functioning apply to both inert and living bodies. In L’Homme, Descartes compared the animal body to a machine, as I discuss later in Chap. 6. Still, although plants should be part of this picture, it is unclear to what extent vegetal bodies fit this comparison. In gathering plants with inert bodies, Descartes separated the former from animals, a differentiation with a meaningful philosophical bearing— this distinction was not uncommon in the early seventeenth century, as, for instance, Bacon and Gassendi highlighted continuities between inert bodies and plants that made it problematic to position plants in the scale of beings.18 Things changed soon after the publication of the Discours—and persisted through the Principia, where Descartes reveals his plans to insert a study of plants together with animals in a section on living bodies. Yet, already in a few notes collected in Excerpta anatomica and dated 1637 Descartes discussed plants and animals together. More specifically, in a note entitled “On accretion and nutrition, November 1637” [De Accretione et Nutritione, 1637. Nov.], Descartes differentiates between inert and living bodies in their ways of growing and provides a very alternative interpretation compared to that of the Discours. Accordingly, while inert bodies grow by accretion, that is, “a simple apposition of particles without any internal change,” living bodies grow by nutrition, which “occurs by means of an internal change [immutatione] of particles” (Excerpta anatomica, AT XI 596) and through the motions of particles within the channels that compose living bodies. At this stage, being fastened to the ground is no longer a criterion to group bodies together. What helps differentiate between bodies is the presence of an internal activity constituting nutrition. Accordingly, in inert or dead [mortuorum] bodies, there is no such internal process, as their growth consists of particles entering from outside and adding to, or replacing the original particles of the body, while in living bodies an internal set of activities produces nutrition, what he called immutatio.19

15

See Baldassarri 2020b. See L’Homme, AT XI 202. 17 Ibid.; G 169: “these functions follow in this machine simply from the disposition of the organs as wholly naturally as the movements of a clock or other automaton follow from the dispositions of its counterweights and wheels.” 18 This point is quite problematic. For Bacon, see Rees 1996. For Gassendi, see Guerrini 2004. 19 Descartes repeated a similar claim, grounded on the internal movement of particles, to the Marquess of Newcastle in 1646; see Descartes to Newcastle, November 23, 1646, AT IV 570–571: “[animals and plants] grow [. . .] by the means of some juice flowing through the little channels in all the parts of their body [while stones] grow by the addition of parts [. . .] from outside and penetrating into their pores” [Translation is mine]. 16

5.1

Classifying Plants

123

Accordingly, nutrition is an act of internal transformation, as nutrients are transformed within the plant, move through its channels, and form the different parts of the plant. The cause or principle is internal to the body, and it is an activity of the plant. Differing from this, any transformation in inert bodies has an external cause. When a dead plant fossilizes, for instance, rocky parts enter it from outside and replace the vegetal ones. Descartes gave this example in the text, differentiating between fossilization (discussed in Sect. 4.2) and nourishment, in which particles compose the wood, bark, roots, leaves, flowers, and fruits in plants, and all the limbs in animals.20 A similar criterion is to be found in the Aristotelian tradition as well. In discussing the vegetative soul, self-change and nutrition, Scholastic philosophers characterized immanence and intrinsicness as acts of living bodies operating within themselves, while nonliving bodies do not act but are acted upon from outside.21 Along these lines, Rodrigo de Arriaga (1592–1667) proposed a more specific criterion to characterize nutrition in living bodies, speaking of intus-sumption or taking within.22 Accordingly, intus-sumption involves particles undergoing a process of internal change, in which the food is transformed into the body, and this is “the clearest and best-known difference between plants and animals and other things [. . .] as plants live [. . .] because they grow and nourish themselves by drawing into themselves sap [succum], food, and so forth” (Des Chene 2000: 62).23 At first sight, Scholastic intus-sumpion is comparable to Descartes’s immutatio, as both are a set of processes regulating the self-change of aliments or particles operated by the body itself. The main difference lies in its principle. While for Scholastic tradition the principle is the vegetative soul, which causes “the conversion of aliment into the living thing’s own substance”24 and regulates the mutations that living bodies undergo, in Descartes, the immutatio is an entirely mechanical process regulating nutrition, self-growth, and generation in living bodies. According to Descartes, the principle of vegetative activities is a mechanical process.25

20

Excerpta anatomica, AT XI, 597–598. Des Chene 2000: 55–66. 22 Roderigo de Arriaga, De Anima, d2§1.1no19, in Arriaga 1632: 636. Translation is from Des Chene 2000: 61–62: “fire grows only through juxtaposition, assimilating matter that is close to it [. . .]; but plants and other animate things do not grow by juxtaposition, but through intus-sumption, that is, by attracting to themselves through their pores food divided into tiny particles, and converting it into themselves; that process occurs, moreover, in such a way that even the more remote parts grow, which is unlike fire.” 23 I thank Stefan Heßbrüggen-Walter for having discussed this passage with me. See Baldassarri 2020c. Bognon-Küss and Demarets 2022. 24 Franciscus Toletus, De Anima, II, chap. 4, L, in Toletus 1985, f. 71va: “reparantur per conversionem alimenti in propria viventis substantiam, quae dicitur nutritio.” Aquinas, Summa contra gentiles, II, cap. 62 n. 8, in Aquinas 1980: 44. Aquinas, In octo libri Physicorum Aristotelis expositio, in Aquinas 1965, VIII, l.4 n.6, p. 520. 25 See Hall 1970: 64. 21

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What results is important. First, the immutatio assumes the role of the principle of vegetative functions, that is, a vegetative power regulating the composition of living bodies through nutrition, as he claims in a letter to Regius.26 Second, in Descartes’s natural philosophy, the immutatio provides a mechanical framework to study the operations occurring in plants. In this sense, plants are bodies performing the basic living activities by means of a vegetative power.27 Third, it appears that in Descartes, vegetative and vegetal overlap, while in the Aristotelian tradition, this coincidence was much more problematic. The role of vegetal processes for defining plants is confirmed in a letter to Alphonse Pollot (1602–1668) of April or May 1638, in which Descartes described for the first time the internal structure of plants in detail (again in connection with animals). Accordingly, nature packs plants “with an infinity of tiny invisible ducts through which certain juices gradually ascend to the ends of the branches, where they intermingle and combine and dry out in such a way as to form leaves and flowers and fruits” (Descartes to Reneri for Pollot, March or April 1638, AT II 40–41; CSMK, 100). In this letter, Descartes suggests that a mechanical activity allows for the formation and fructification of plants, namely the main operations of vegetal bodies. The mechanical power discussed in the note is what makes a plant a plant, that is, a body performing vegetal processes by means of nutrition, formation, growth, and generation. This is later confirmed in La Description du corps humain, where he claims that “living bodies [. . .] are maintained through nourishment, that is, animals, and plants, undergo continual change” (La Description du corps humain III, AT XI 247; G 183).28 Developing from this definition of plants, a discipline of botany consistent with his philosophy would focus on the study of such vegetal processes. From the end of 1637 and early 1638, Descartes secured the interpretation of plants as living bodies on the mechanical operation of growth. Differently from rocks, minerals, and metals, whose accretion is a mere apposition of parts, the processes of vegetation characterize plants and animals as possessing an internal mechanical principle, the immutatio, operating on the self-maintenance of the body by transforming the particles of food into the body. As a result, animals and plants share similar mechanical operations and the same mechanical framework.

26 Descartes to Regius, May 1641, AT III 372: “Vis autem vegetativa [. . .] nihil aliud est quam certa partium corporis constitutio”. See Baldassarri 2021c. 27 This is the definition provided by Regius, though he speaks of a material vegetative soul, see Regius, Fundamenta physices: 148. 28 It is to be noted that this point is anticipated in L’Homme, where it remained unexplored. Descartes writes that “one observes the same thing in plants, [. . .] this is a property that seems to be common to all bodies which are able to grow and be nourished by the union and joining together of the tiny parts of other bodies” (L’Homme, AT XI 201; G 168).

5.1

Classifying Plants

5.1.2

125

A Mechanical Gradation Between Plants and Animals

Yet, another note of Anatomica and a letter to Mersenne help us grasp his interpretation of plants in relation to animals better, nuancing his understanding of living nature. The note is collected in both Primae Cogitationes and Anatomica and is probably from the same period as the note discussed earlier. Here, Descartes described that: The formation of plants and animals is similar by taking place through the circular movement of particles of matter under the force of heat; but it differs in that, in the generation of plants, the particles of matter revolve circularly, while those particles generating animals revolve spherically and in all parts. (Primae Cogitationes, AT XI 534)29

While the same mechanics of the motion of particles applies to the generation of plants and animals,30 as the soul plays no role even in this case,31 Descartes provides a differentiation between living bodies. The difference resides in the motions of particles, which he reduced to a geometrical pattern: Vegetal particles revolve circularly, while animal particles revolve spherically. Accordingly, this difference depends on the fact that “the particles of [fetus] revolve spherically producing a round tunic that includes the fetus, and therefore it does not adhere to the soil, as plants do” (Primae Cogitationes, AT XI 595; Leibniz SSB: 574). This difference appears consistent with the fact that plants adhere to the soil, while animals do not. The former thus grow in one direction, upward from the ground, which is what the circularity of motions describes (see Fig. 5.5, later in this chapter), while animals grow in all directions. The movement of particles during generation thus defines their liberty of motion, showing a mechanical degree of freedom that entails a mechanical differentiation, if not even a gradation. This is a significant point. If earlier being fastened to the ground (and being unable to move) allowed Descartes to claim a continuity between plants and minerals, in this note he did not follow this path and gathered animals and plants together. This is confirmed by the same mechanical rules that regulate their generation, but a difference in freedom ultimately reveals a mechanical gradation between animals and plants. Another aspect surfaces in an August 1638 letter to Mersenne concerning the movement of the leaves of the sensitive herb, the mimosa pudica.32 In this letter, Descartes stretched the animal–plant analogy further. He claims to be able to account for vegetal sensitivity as the same mechanics regulating animal sensitivity applies to this plant, if similar organs are within it. He writes that:

Original Latin is: “In eo convenit formatio plantarum et animalium quod fiant a partibus materiae vi caloris in orbem convolutae, sed in hoc discrepant, quod partes materiae ex quibus plantae generantur volvuntur tantum in orbem circulariter; eae vero ex quibus Animalia volvantur sphaerice et in omnes partes.” 30 Baldassarri 2018b. 31 Des Chene 1996: 138–156. Hirai 2011. 32 See Giglioni 2018. 29

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I do not find anything curious except its rarity; for, having explained the movement of the heart in a way which suits both plants and animals, I will have no difficulty in conceiving how it moves if the same organs can be found in that plant. But I do not want to say more clearly how this movement occurs, as I have not observed or examined it. (Descartes to Mersenne, 23 August 1638, AT II 329)33

As already shown, in this letter, Descartes tested the validity of the animalmachine model for the knowledge of plants, recognizing the similarities between these bodies. The same processes characterize not only plants and animals but also a similar theoretical framework. However, a complete identity between animals and plants (valid for the singular case of plant sensitivity, but also in general) should be confirmed by observations, that is, by means of a posteriori knowledge—something that, however, Descartes could not attain at this stage. Descartes did not pursue this point, and a difference remains. Although plants and animals are similar machines, they have a different structure with different organs. This is a crucial limitation to the mechanical analogy between plants and animals, and Descartes did not use the case of the sensitive herb to bridge the gap between animals and plants—Regius will later claim that the sensitive herb is a zoophyte, a definition rejected by Descartes. In sum, plants are a shifting subject in Descartes’s natural philosophy. While in the early 1630s he probably conceived them just as inert bodies, mostly because both acquired matter from outside and are fastened to the ground, from late 1637 and early 1638 Descartes defined plants as vegetating bodies (especially through his interpretation of a mechanical power of the body, the immutatio), revealing a mechanical analogy with animals. In this case, a mechanical interpretation of their functioning plays a decisive role in defining their similarity and their functioning. In both animals and plants, growth is an internal activity, with an internal principle or power, quite different from minerals and metals. Still, he could not completely overlap plants and animals, and some crucial differences remain—both mechanical differences (the diverse movement of particles in growth) and organic differences, which reveal a sort of gradation between bodies.34 A more detailed interpretation of plants emerges in Descartes, as plants are certainly different from inert bodies but also present several differences from animals. From Descartes’s work in 1637, plants appear, however, closer to animals, for a similar mechanics regulates their functioning, and similar functions surface— namely vegetation. Yet, it is necessary to specify their mechanics and how much they differentiate from inert bodies. In the next section, I investigate Descartes’s botanical collaborations, as he performed several botanical observations to fill that gap, while in the third section, I disclose his study of the mechanical functions of plants.

33 34

See Gaukroger 2002: 187. On the comparison, see Sect. 2.2.1. As I show in Chap. 6, a limitation to the mechanization of animals significantly arises.

5.2

Descartes and the Dutch: Corpuscles, Catalogs, Observations, and. . .

5.2

127

Descartes and the Dutch: Corpuscles, Catalogs, Observations, and Botanical Gardens

Before focusing on Descartes’s observations, let us explore the Dutch context, in which Descartes was immersed, and the ways in which Dutch scholars dealt with plants. In the early modern period, the Netherlands was a dense zone of information exchange, favored by the commerce of the time, in which plants attracted varied attention from trained scholars and untrained people interested in exotic and beautiful flowers. As Alan Morton has shown,35 combining the natural historical enterprise, the enthusiasm of collectors, and the scientific performances of experimenters, the early modern Dutch Republic was a suitable place for the achievement of a science of botany, as the cases of Rembert Dodoens (1517–1585), Mathias de Lobel (1538–1616), and Carolus Clusius (1526–1609), among others, reveal.36 These figures combined the attention to collecting, naming, accommodating, and cultivating with the performance of direct observations to grasp the nature of plants in botanical gardens. In building a science of plants out of the practices of exchange, collection, and experimentation,37 Dutch scholars embraced and developed Francis Bacon’s empiricism, which concerned botany as well as other disciplines. While the Dutch context is an important key to understanding botanical experimentation in the seventeenth century and deserves to be studied in itself, in this section, I focus on four spheres that influenced Descartes’s study of plants: (1) corpuscularianism, (2) Baconianism, (3) catalogs and gardens, and (4) microscopic observations.38 The first case is represented by Isaac Beeckman, who provided a corpuscular study of plants in his Journal, an application of his corpuscularian understanding of bodies that was well known by Descartes. The second case is represented by the circle of Huygens, who corresponded on Baconian botanical experiments with Johan van Brosterhuysen (ca. 1596–1650). The circulation of catalogs and specimens, whose centers were botanical gardens, represents the third case. Finally, I discuss the microscopic observations of plants Descartes performed with the help of Henricus Reneri, taking place within a clear Baconian tradition.

5.2.1

Isaac Beeckman

Beeckman played a central role in the scientific knowledge developing in the Dutch Republic, especially since he devised a physico-mathematical philosophy to 35

See Morton 1981: 165–178. On the role of collaborations and exchanges in botany, see MacGregor 2018. Cf. Anagnostou et alii 2011 and Egmond 2018. 37 See Egmond 2017b. 38 For a broad investigation of the reception of Descartes’s philosophy in the Dutch Republic, see Verbeek 1992b. 36

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investigate nature that influenced, if not even inspired, Descartes.39 Beeckman’s remarkable attempt to account for natural phenomena and bodies within a systematic theory of mathematical physics combines mechanical ingenuity, mathematical methodology, and the study of particular bodies within a theoretical view. In his Journal, an outstanding laboratory in which practices and ideas were studied under different perspectives,40 he also discussed plants, although he was certainly neither a botanist nor a botanical virtuoso.41 In this section, I aim to discuss a few of these entries. In a 1628 entry, Beeckman commented on two experiments from Bacon’s Sylva Sylvarum, namely experiment 601 and experiment 607,42 which deal with the difference between animals, plants, and metals.43 This note is part of a larger section of the Journal in which he discussed Bacon’s experiments on sound and light in the Sylva Sylvarum and contains an atomistic-corpuscular interpretation of these phenomena.44 Within this corpuscular framework, Beeckman explored the nature of spirits endowing particular bodies such as metals, plants, and animals and considers these spirits to be material. More than a note on plants in their own right, or a note on botanical experimentation, this is a comment on what differentiates inert from living bodies, a crucial question at the time. Beeckman’s note concerns the presence of spirits that ignite within bodies. This is connected to his claim that life corresponds to a fire in bodies, as he writes one page after this note, in the margin to Sylva’s experiment 704.45 In commenting on experiment 601, Beeckman synthetized two ways to differentiate between inanimate and animate bodies. This first resides in the fact that plants and animals have spirits in branches, veins, and little channels that are within the body, thereby moving throughout it, while spirits in metals and stones are in little holes and do not come together or move. Bacon stated that spirits in living bodies “are continuous with themselves” and communicate, while inanimate bodies “are shut [. . .] and not pervious one to another,” or communications between spirits are interrupted. The second difference consists in the fact that the spirits in living bodies are ignited and burn, while spirits in inert matter are more difficult to ignite, even though they possess much hotter spirits, as the cases of naphtha, petroleum, and spices show. Following Bacon, Beeckman stressed that the spirits in living bodies are quicker to ignite, while those in inert bodies are more difficult to ignite, but once they do ignite, they have more heat substance in them, and the burning is fiercer. In commenting on experiment 607, Beeckman acknowledged Bacon’s division between animals and plants. Accordingly, spirits in animals have a position,

39

On Beeckman and Descartes, see Sect. 2.2.2. Dibon 1990. van Berkel et al. 1999. The Dutch Republic as a laboratory of early modern science is in van Berkel 2010. 41 On a broader study of Beeckman’s botany, see Baldassarri 2022b. 42 Bacon, Sylva Sylvarum: 528–529. 43 Beeckman, Journal, III, 64. 44 See Dibon 1990: 193–199. Alberto 1991. Gemelli 2013. 45 Beeckman, Journal, III, 65: “Vita nostra quomodo sit ignis.” 40

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something that Bacon calls “a Cell or Seat,” which is absent in plants, and for this reason ignite much more than in plants. This is what Bacon considered a radical difference between living bodies. Beeckman appeared, however, to be dissatisfied with this explanation and suggested investigating more thoroughly the spirits in stones, since their properties might depend on “a vacuum” or on the density of these bodies. Beeckman did not mention the eight secondary differences between animals and plants listed by Bacon in Sylva, and appeared therefore less interested in plants in themselves. His primary concern is with the presence of spirits in natural bodies and in the differences in bodily flammability. In following a more theoretical approach to vegetal bodies, he used them as laboratories to explore spirits and flammability. It is no surprise, then, that in an earlier note of the Journal, while discussing fires, Beeckman presented the case of a particular plant, namely the noli me tangere, which in this case is not the sensitive herb discussed by Descartes and Mersenne, but the herba impatiens. Beeckman described the explosive dehiscence or process of spontaneous bursting of plant structures, especially connected with the release of seeds.46 As happened with several exotics at the time, it was not easy to find this plant in the Dutch Republic, and it is probable that Beeckman did not achieve any direct observation of it.47 Yet, since the phenomenon was known and studied, he reduced it to the corpuscular structure of light, conceiving the bursting phenomenon as a suitable example to describe natural bodies, resulting in a theoretical approach to plants. In other notes, Beeckman dealt with the ways plants grow.48 He claimed that trees grow by means of the movement of particles of humors drawn from the soil by a sort of attraction and by the heat of sunrays. The latter enlarge the pores of the plant and prepare or cook the humors, converting them into the substance of the plant. As these particles move toward the top of the plant, they make it grow upward. It is to be noted that, since plants are cold bodies, they mostly grow during the summer, while animals grow perpetually thanks to their internal source of heat. More precisely, Beeckman acknowledged nutrition in plants as a conversion of humor into the parts of the plant, activated by what he calls a returning heat, which is probably the heat of the sunrays that make the humors melt within plants. At the end of the note, in contrast, he spoke of a calido innato endowing all living bodies. Nevertheless, he clearly stressed that what makes humors arise within the plant is a sort of attraction presumably produced by the fact that the sunrays widen the pores of the plants, and this enlarged space attracts the humors from the bottom parts of the plant and from

46 Bauhin, Pinax: 306–307: “Noli me tangere & Impatiens herba . . . quae ubi maturae levissimo contactu dissiliunt. . .” Dodonaeus, Stirpium: 648–649: “Belgae Crudeken en ruert my niet: vulgo Noli me tangere. . .” 47 Egmond 2010: 36. One should note that Nehemiah Grew investigated a similar case of a plant violently discharging the seed in Anatomy of Plants, 188–189. See Bertoloni Meli 2016: 102. 48 Beeckman, Journal, I, 284.

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the earth. Beeckman claimed that this enlargement of pores creates a vacuum that makes humors rise as happens in air pumps.49 Beeckman confirmed the role of these motions in several other notes, as he explained why trees grow taller in regions with fresh water, whereas plants that grow larger are abundant in areas close to the sea, where water is mixed with salt.50 In a note on grafting of May 1626, Beeckman described that “elements change in everything, and the humors of the trunk or rootstock are converted in their nature by the scion or grafted branch, thanks to the different positura of the particles of the scion” (Beeckman, Journal, II, 341–342). While passing through one plant to another, the particles of the humors take a different arrangement, what he calls positura, and constitute the plant, according to Beeckman. The mechanical motion and change of particles that take different shapes and their arrangement throughout the body explain the formation of plants in Beeckman’s mechanical philosophy of nature, thereby detailing several cases, such as the growth of plants, herbs, and shrubs, and the case of grafting. It is to be noted that the heat of the Sun and freshwater favor the motions of humors and particles deriving from the earth, passing through the channels and pores of plants and taking different shapes and positions, thereby resulting in the formation of vegetal bodies. Still, Beeckman did not observe this change in the form of particles, nor did he explain what operations plants undergo within. Beeckman’s mechanic-corpuscular framework in the study of plants appeared significant at the time, despite the fact that his interest in plants remained marginal and unsystematic—thus congruent with Descartes’s criticism of Beeckman’s Journal disclosed in Chap. 2. Whether these notes inspired Descartes’s investigation of plants is, however, difficult to claim, but they uncover a clear example of the Dutch experimental approach to vegetation in the late 1620s and early 1630s that was not dissimilar from Descartes’s approach and certainly influenced the context in which Descartes achieved his study of plants.

5.2.2

Huygens and Brosterhuysen

Circles of learned scholars and virtuosi burgeoned in Holland at that time. An outstanding representative of the boundless interests of Dutch virtuosi is Constantijn Huygens, one of the best friends of Descartes in the Dutch Republic, who certainly appreciated the anatomy of bodies à la Descartes, as well as Bacon’s experimentation with nature.51 Both the entertaining value of plants and the attraction to vegetal

49

Beeckman, Journal, I, 23. Cf. Van Berkel 2013: 85. Beeckman, Journal, I, 130. 51 Huygens to Descartes, 7 July 1645, AT IV 779: “depuis votre Philosophie aucunement comprise, je deviens de plus en plus amoureux de l’anatomie des choses.” See Chap. 4 on this letter. On Huygens and Bacon, see Rees 2002: 380. 50

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rarities and exotic specimens, as well as the fabrication of perfumes, extracted essences, and therapeutics, reveal the variety of Huygens’s fascination with plants.52 But Huygens also corresponded on Baconian experiments with plants. This especially surfaces in Huygens’s correspondence with Brosterhuysen, a Leiden artist and botanist, and a protégé of Huygens.53 As soon as Brosterhuysen received Bacon’s Sylva Sylvarum in 1629, he made a few comments on his botanical experimentation, starting by declaring his appreciation of Bacon’s “very gentle way of considering the nature of things,” as he “develops experiments with sound and useful consequences” [Brosterhuysen to Huygens [end of] February 1629, in Briefwisseling vol. 1, 254.] The first is experiment 769 of Sylva, which concerns the class of “plants without leaves.” Yet, Brosterhuysen noted that, in describing “the rose of Jericho [. . .] that has big leaves, and [is] full of juice,” Bacon’s case study is incongruous with the class of investigation. Accordingly, Bacon appears “misinformed about the nature of this plant” (Brosterhuysen to Huygens [end of] February 1629, in Briefwisseling vol. 1, 254) while Brosterhuysen himself had cultivated it and certainly knew it in detail.54 In correcting Bacon, the Dutch botanist named a few plants having branches without leaves that suited the case better, for example a kind of hippuris, “that is [. . .] our schuijrstroo, then l’uva marina, but also the noble salicornia, from whose ashes we make the sal alkali, which has the power to facilitate generation and abortion.” All of them would apply better to the case. Indeed, the latter perfectly fits the description of Bacon’s experiment. Brosterhuysen then made other examples, informing Huygens that “prickly pear is a plant made of nothing but leaves,” and suggested looking for its outcomes, “which should be greatly extraordinary” (Brosterhuysen to Huygens [end of] February 1629, in Briefwisseling vol. 1: 254). The second is experiment 636 and concerns excrescences growing on trees. Again, Brosterhuysen denied Bacon’s claim that the agaric, a type of mushroom, “groweth on the top of oaks.” In contrast, he suggested that this mushroom “grows only on larches, and only on the trunk” (Brosterhuysen to Huygens [end of] February 1629, in Briefwisseling vol. 1, 254).55 The third is experiment 390, dealing with odors and showing some utility for distillations. A month later, Brosterhuysen replicated experiment 408, in which Bacon suggested putting a Dutch flower into water.56 This is a way to accelerate germination, as Brosterhuysen confirmed.

52

See Colie 1956: 135–136, 142. Held 1991. Baldassarri 2020c: 659–662. There is no evidence of a direct contact between Brosterhuysen and Descartes, yet the former knew Descartes’s work well, due to his friendship with Huygens, Hortensius, and John Pell. See Malcolm and Stedall 2005. See Descartes to Wilhem June 15, 1646, AT IV 435–436. 54 Cf. Bacon Sylva Sylvarum, exp. 769, p. 588: “there is also in the desert [. . .] a plant which is long, leafless, brown of colour.” One should note that in the seventeenth century, the rose of Jericho was a monstrous plant, as people believed it could resurrect. As it appears, Brosterhuysen was not interested in this side of the story. 55 Cf. Bacon Sylva Sylvarum, exp. 636, p. 537. 56 Bacon, Sylva Sylvarum, exp. 408, p. 478: “A Dutch flower that had a bulbous root, was likewise put at the same time all under water, some two or three fingers deep; and within 7 days sprouted, and continued long after further growing.” 53

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Indeed, “the bulb starts pushing [germinating] the flower, whose season would be not before a month” (Brosterhuysen to Huygens March 29, 1629, in Briefwisseling vol. 1, 257). The interest in bulbs and flowers (and especially in tulips) and in making them sprout at different periods of the year was widespread in early modern Holland. In this correspondence, Brosterhuysen conducted observations following Bacon’s text and demonstrated his experiential ability as a botanist to Huygens while he was trying to secure a stable position in Utrecht or Amsterdam. However, Brosterhuysen’s early ambitions to be put in charge of the botanical gardens in both cities came to nothing, but he later set up a medicinal garden in Breda.57 Brosterhuysen’s investigation of plants put aside the attraction for naturalia or rare specimens that was rife throughout Dutch culture and was more focused on direct observation of vegetal bodies. His approach thus combined (1) botanical knowledge with (2) Bacon’s experiential method and (3) the chymical investigation of nature. This reveals the eclectic ways of performing experimentation of Dutch botanists as a combination of expertise that ranges from gardening and botany to chymistry and pharmacology. Yet, this short correspondence also reveals the unsystematic approach to botanical experimentation, as Brosterhuysen performed observations to complete or correct a theory, to reject a result, or to explore if a new effect was possible. As in the case of Beeckman, Brosterhuysen and Huygens appeared more interested in discovering effects, than in laying bare the causes of vegetal life. For instance, in the only reference to plants in the correspondence between Huygens and Descartes concerning the ambretta flowers,58 the former’s reply is illuminating. Indeed, he sent Descartes some seeds of ambretta, stressing that its “flower is nobler than coriander, less beautiful [. . .] but more scented [. . .] and when cut and put into water, it conserves its grace longer than any other flowers I know” (Huygens to Descartes, January 7, 1647, AT IV 790 [translation is mine]).59 This short note shows Huygens’s familiarity with botanical experimentation in line with the Baconian framework, as this experimentation aimed at knowing the diverse effects one could produce to increase the virtues of plants and flowers. Accordingly, Dutch botanical empiricism geared to the knowledge of effects one could observe, without a clear systematic grasp of the nature of plants, was a kind of knowledge with little attraction to Descartes, although he certainly praised the experimentation with bodies.

57

Brosterhuysen, Catalogus. See Dibon 1990: 199–201. Descartes to Huygens, November 30, 1646, AT IV 788. 59 Original French is: “Ce sont les grains de nos Ambrettes, dont si vous ne connaissez la fleur, sachez que c’est une Corien-blom d’extraction noble, et que si elle cède à la commune en beauté, elle la surpasse en odeur et durée; car même après sa mort, j’entends quand elle est coupée et entretenue dans l’eau, elle garde sa grâce plus longtemps qu’aucune autre fleur que je sache. . .” They are referring to Knautia arvensis. Probably, Descartes’s interest lies in its scent, but it could also be in the oil one could draw from it. 58

5.2

Descartes and the Dutch: Corpuscles, Catalogs, Observations, and. . .

5.2.3

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Circulating Seeds and Catalogs

Descartes was not outside the circle of exchanges of seeds and plants, as the letter to Huygens reveals. Yet, there is more. In the late 1630s, Descartes had indeed exchanged several other specimens, both with Mersenne and with his Dutch peers. In October 1639, Mersenne offered Descartes a few seeds of the sensitive herb.60 In November, Descartes stated that someone at the Leiden botanical garden tried to cultivate that plant without any success, despite the fact that it was the correct period to sow it.61 It is probable that Descartes had discussed the mimosa with someone at the Leiden botanical garden, and even how to accommodate and cultivate it, as he wrote to Mersenne in March 1640: “I am grateful [. . .] for the seed of the sensitive herb that I have now received, and we will cultivate it with care” (Descartes to Mersenne, March 11, 1640, AT III 40 [italics mine][translation is mine]).62 At the same time, Descartes proposed an exchange of botanical catalogs to Mersenne. The latter should send him the catalog of the Parisian Jardin du roi (namely the Description du Jardin des plantes medicinales, 1636) and Descartes would send in return the catalog of Leiden Hortus Botanicus, which “someone offered to give to [him]” (Descartes to Mersenne, November 13, 1639, AT II 619 [translation is mine]). Probably, this text is the Catalogus plantarum horti academiae Lugduno-Batavae prepared in 1633 by Adolphus Vorstius (1597–1663), the director of the garden, who befriended Descartes. At this time, Descartes appeared to be at the center of a network of exchange of the seeds of the mimosa as well as of catalogs. In June 1640, he claimed to have provided several people with seeds: “the seeds of sensitiva have not sprouted in any place yet, although I gave them to people who sow them with great care” (Descartes to Mersenne, June 11, 1640, AT III 78 [translation is mine]).63 Additionally, he was in contact with Anthony Studler van Zurck (c. 1608–1666), with whom Descartes discussed the seed,64 and who was an intermediary between Descartes and Vorstius.65 Finally, in a September 1640 letter to Mersenne, Descartes stated that “the seeds of the sensitive herb you sent us have not sprouted at all; but thereafter, we have received some more from the Indies which sprouted in little time in the garden of a man, where I saw it, who had planted some 60 Descartes to Mersenne, October 16, 1639, AT II 595; Descartes to Mersenne December 25, 1639, AT III 633. 61 Descartes to Mersenne, November 13, 1639, AT II 619. 62 Original French is: “[J]e vous remercie très humblement de la graine de l’herbe sensitive, que je viens tout maintenant de recevoir, et nous aurons soin ici de la cultiver le mieux qu’il se pourra.” 63 Original French is: “Les graines de l’herbe sensitive ne sont point encore levees en aucun lieu, quoique j’en aie donné à plusieurs qui les ont semées curieusement.” 64 Descartes to Van Zurck, November 26, 1639, AT II 713–714. 65 Descartes to Vorstius, June 19, 1643, AT III 686. It is to be noted that in 1643, Descartes and Vorstius exchanged a text on rabies, likely Giuseppe degli Aromatari’s (1587–1660) Disputatio de rabie contagiosa (1625), which includes an epistle on the generation of plants from seeds, i.e., the Epistola de generatione plantarum ex seminibus, containing a hypothesis on preformation (see Verbeek et alii 2003: 90–92.)

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more” (Descartes to Mersenne, September 15, 1640, AT III 176 [italics is mine] [translation is mine]).66 Who these people are is regrettably unspecified, although they could have been some botanists or Dutch botanical enthusiasts. Descartes was clearly in contact with them as they cultivated and observed the sensitive herb together. Descartes did not appear completely estranged from a context sometimes inspired by and modulated through the Baconian tradition, but he made clear his aims. When he rejected the utility of the catalog of the Jardin de plantes, which is “of little use [. . .] since it contains only names, [whereas he was] looking for things” (Descartes to Mersenne, June 11, 1640, AT III 73) [translation is mine])67 what arises is (1) Descartes’s familiarity with catalogs and botanical gardens, (2) the necessity of a description of things for furthering experimentation, and (3) his interest not in collecting varieties but in dealing with particular bodies to experience what mechanical physics had established on a pure theoretical level.68 A material study of bodies, a direct observation of their activities, the possibility to sow and cultivate plants (in botanical gardens), and to know them through catalogs and through the discussion and help of peers characterize Descartes’s investigation of plants in the Dutch Republic, but appears ancillary to the mechanical systematization of plants.

5.2.4

Henricus Reneri

Descartes’s observations of vegetation especially surface in his work with Reneri, a good Dutch experimenter, reader of Bacon, and one of the closest friends of Descartes in the Dutch Republic. In 1637, Reneri delivered copies of the Discours to Hooft, who maintained a circle of erudites that included Huygens and Brosterhuysen. At the same time, Reneri was part of the Hartlib circle, one influenced by Bacon, and proposed a clearly Baconian program of education at Utrecht Illustrious School (later Utrecht University).69 In the winter of 1637–1638, Reneri joined Descartes in Santpoort, where they studied geometry and pursued many observations on natural bodies, especially on vegetation. Apparently, this collaboration had been inspired by Descartes’s suggestion that microscopic investigation of natural bodies could usefully help the observation of their nature, as “the different mixtures and dispositions of the small parts that make up animals and plants [help] acquire a great knowledge of their nature”

66 Original French is: “Toute la graine de l’herbe sensitive que vous nous avez envoyée n’a point levé; mais on en a reçu d’autres des Indes longtemps depuis, laquelle leva en fort peu de temps, dans le jardin d’un homme où je l’ai vue, et qui en avait aussi semé de l’autre.” 67 Original French is: “[C]e livre [. . .] est peu à mon usage, car il ne contient que des noms, et je ne cherche que des choses.” 68 Descartes to Mersenne, December 25, 1639, AT II 633. 69 Buning 2013: 181–184. On the Hartlib circle, see Matei 2015.

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(Descartes, La Dioptrique, AT VI 226 [translation is mine]).70 In Santpoort, the two probably used the microscopes, or lunette à puce recently fabricated by Reneri. Although we do not have notes on this collaboration, in two letters sent to David le Leu De Wilhem (1588–1658) and Mersenne in late February and early March 1638, Reneri envisaged a program of research and made clear what he had been doing during his winter vacation with Descartes. In these letters, Reneri both enhanced the intellectual exchange with Descartes on mathematical knowledge and presented a few observations to examine the nature of plants. The most interesting part is in the middle of the letter, where he claims that: [t]o this effect [i.e., for the study of plants], I will mix together all sorts of soils in order to see the different effects: next, I will acquire diverse seeds, observe them from the outside and from the inside with a lunette à puce of my invention, I will soak [seeds] in diverse solutions, then I will sow them. Once sowed, I will examine them and observe as carefully as possible their diverse ways of sprouting, growing their first roots, buds, leaves, flowers, fruits or seeds, etc. (Reneri to De Wilhem February 28, 1638)71

This section reveals a Baconian project for botanical investigation. Besides the general influence of Bacon on Reneri, the latter possessed Francis Bacon’s Sylva Sylvarum,72 a text with a remarkable number of botanical observations that concern the examination of soils, seeds, and the attempt to soak seeds in different matters and solutions in order to observe what effects result—therefore not differently from the cases examined earlier. Yet, Reneri’s interpretation of nature differs from Bacon’s and takes a Cartesian bent, as surfaces in the letter to Mersenne. In this letter, he writes that: I am taken up with making observations on plants and animals. And how fortunate that I can favorably carry these out through new eyes [i.e., a microscope], devised by my art, and I observe seeds, buds, leaves, and flowers that no Ancient, who ignored microscopes, could observe. [. . .] Especially, the conversation with Mr de Cartes increases my amusement [in doing observations]. (Reneri to Mersenne early March 1638)73

A combination of Descartes’s mathematical and optical knowledge with Reneri’s technical abilities in devising instruments to perform observations spurred a mechanical exploration of living nature. In mid-March of 1638, Reneri tabled a disputation

70

See Verbeek 1993. In Buning 2013: 256: “A cet effect je m’en iray composer toutte sorte de terres pour en voir les divers effets: puis je m’en vay prendre diverses semences, les examiner par le dehors et par le dedans avec une lunette à puce de mon invention, je les vay tremper en divers liqeurs, puis semer. Estant semees je m’en vay regarder et observer le plus exactement qu’il me sera possible leur diverses facons de gemer, de pousser leur premeres racines, surgeons, feuilles, fleurs, fruits ou semences etc.” 72 Dibon 1990: 205–218. 73 In Buning 2013: 255: “[T]otus sum in observationibus faciendis circa plantas et animalia. Et quò felicius eas facere possim oculos novos arte mihi paravi, quibus fretus ea. in seminibus, in germinibus, in foliis floribusque deprehendo quae nemo Veterum ob microscopiorum ignorationem observare potuit. [. . .] Praesertim verò voluptatem meam auget conversatio cum D. de Cartes quâ felici quodam sydere fruitus sum et subinde adhuc fruor.” 71

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at Utrecht in which the discussion of plants took an unmistakably Cartesian turn. This is the Disputatio physica continens theses aliquot illustriores, and the respondent was Antonius Mudenus, who was a student of medicine who graduated in 1641 under the supervision of Willem Stratenus. In the disputation, they rejected a few physiological traditional claims, i.e., the role of substantial forms, attractive faculty, and vegetative (and sensitive) soul. The disputation begins with an explanation of plants that seems Cartesian: In plants, besides the matter and its various accidental disposition, and the alimentary juices, it is not necessary to posit any substantial form that works as a principle of the operations of plants (Reneri Disputationum physica: th.1 [translation is mine.])74

It is to be noted that, in two previous disputations held in 1635, Disputationum physicarum secunda, De corpore naturali in genere, and Disputationum physicarum quarta, de elementis, Reneri took the traditional position that bodies are composed of matter and substantial form, while in 1638 hylomorphism is clearly rejected. As he describes the nature of plants with more attention, Reneri denies the existence of the vegetative soul and the vital principle of Aristotelian tradition and endorses an explanation grounded on the matter and disposition of particles and the movement of alimentary juices to explain the nature of plants, their growth, and formation.75 The position held by Reneri is a mechanical interpretation of plants consistent with Cartesian philosophy. Moreover, in the disputation, Reneri claimed that nutrition does not produce a substantial mutation, but it is a mere change in the body. Accordingly, “plants do not have a faculty of attraction of food” (Reneri, Disputationum physica, th. 7 [translation is mine]),76 similarly to all living bodies, insofar as no faculty could be found in bodily organs.77 Besides the rejection of traditional faculties, this passage reveals the importance of observing bodies in order to support a mechanical interpretation of living activities such as nutrition and growth (the disputation also contains a discussion of sensation, imagination, and perception) as well as an interpretation of the nature of plants in the mechanical terms of Descartes’s physiology. In August 1638, Reneri visited Descartes in Santpoort again. Robin Buning has reported that the two discussed a lot of mathematics and natural philosophy at that time.78 These discussions provided the framework for their mutual interest in the observation of plants. In the correspondence of this period, Descartes claims to have performed experiments in his garden, both with seeds and with plants, in line with Reneri’s plans described in the early letter to De Wilhem. While August is an ideal Original Latin is: “In plantis praeter materiam & ejus varias dispositiones accidentarias, & succum alimentarium nullam formam substantialem ponere est necesse, quae sit principium operationum plantae.” 75 See Buning 2013: 161–162. 76 Original Latin is: “Plantae nullam habent facultatem alimenti attractricem. . .” 77 See Reneri, Disputationum physica, th.8–9. 78 See Buning 2013: 205–206. 74

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moment to achieve experimentation in gardens, regrettably no clear evidence of further collaborations emerges. Noteworthy is that the collaboration with Reneri inserts Descartes into the botanical context of Dutch experimenters. In many respects, this context was Baconian. Reneri’s program of studying plants reveals this influence, as he followed Bacon’s methodology of accumulating observations and put in practice the experiments described in Bacon’s Sylva Sylvarum aiming at collecting effects and results. Reneri possessed a well-furnished library concerning experimentation with plants from which they could have drawn examples to be repeated. Besides Bacon’s Sylva Sylvarum and the Historie naturelle (Paris, 1631), his library included Daniel Sennert’s (1572–1637) Hypomnemata physica (Frankfurt, 1636), and Giambattista Della Porta’s (1535–1615) Magiae naturalis (Frankfurt, 1607). A link may be drawn between these books, as their authors suggested performing similar observations, although with different aims and purposes.79 Although there is no clear evidence that Reneri and Descartes read these texts or replicated any experiments from them, it is probable that they knew some of their contents and accommodated such observations on plants within Descartes’s geometrico-mechanical physics. In this sense, while Descartes took advantage of Reneri’s expertise in performing experiments on seeds and plants in order to collect observations on the nature of things in a Baconian perspective, he provided Reneri with a theory of matter to strip nature of substantial forms, inner qualities, vital principles, and souls, that is, a clear philosophical aim. In sum, in welcoming the importance of observations that characterized the Dutch approach to plants, Descartes’s goal was to grasp the causes of plants functioning and mechanical life, not merely focusing on the effects of experimentation, ultimately illustrating a precise interpretation of nature.

5.3

The Mechanical Physiology of Plants

In Excerpta anatomica, Descartes’s study of plants takes shape. Developing from the observations he performed throughout the years, in these notes he grappled with plant life, generation, nutrition, formation, and production of fruits from a mechanical perspective. The mechanization of vegetal activities in these notes is possibly the subject of a section on plants in Descartes’s natural philosophy.

79

On the connection between Bacon, Della Porta, and Sennert, see Rusu 2017; Jalobeanu 2018b. See also the articles in a recent special issue edited by Rusu and Jalobeanu 2020.

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Plant Generation

The first note is from both Primae Cogitationes circa generationem animalium and Excerpta anatomica. Although the original texts present a few minor differences, I report the text of Adam-Tannery.80 This is the note: The formation of plants and animals is similar by taking place through the circular movement of particles of matter under the force of heat; but it differs in that, in the generation of plants, the particles of matter revolve circularly, while those particles generating animals revolve spherically and in all parts. (Primae Cogitationes, AT XI 534)81

Despite never referring to seeds explicitly, in this note Descartes writes of generation and of the fetus, and this part actually describes the formation of living bodies from their seeds. According to Descartes, analyzing how plants gradually grow from seeds is as fundamental to knowing their nature as it is for animals and human beings.82 This text presents several issues. First, Descartes claimed that the generation of plants and animals relies on the movement and disposition of particles produced by the force of heat. This reveals a great distance from the usual discussions of generation in his time.83 Traditionally, the main question of generation concerned the reception of a determinate form in matter, or the presence of a soul in the fetus. This was also the case with plants. Pierre Gassendi, for instance, explicitly referred to the soul, a seminal force endowing seeds.84 In contrast, Descartes did not mention souls or seminal forces but focused on the material movement and arrangement of particles to explain generation.85 Second, Descartes differentiated the formation of plants and animals following a geometrical distinction. As previously seen, he distinguished between two movements of particles: a circular motion in the formation of plants and a spherical motion in the formation of animals. In the first case, particles follow one direction, as they only revolve circularly. Accordingly, particles revolve from point a to point b (see Fig. 5.3). In the second case, particles follow different directions and revolve spherically, following different lines and therefore composing a more complex body. Since plant particles move in a circle, this movement is consistent with the theory of vortices. Vincent Aucante has recently stressed the similarity between the motions of particles during generation and the three laws of motion in Le Monde.86 Still, this note adds something more, detailing the different motions—circular and 80

While AT considers the note of the Excerpta to be identical to the one of the Primae Cogitationes, both textual and paratextual differences arise. I am not going to examine these differences here. 81 See note 29 above for the Latin original. 82 Principia philosophiae, III, art. 45, AT VIII-1100; MM 105: “just as for an understanding of the nature of plants or men it is better by far to consider how they can gradually grow from seeds.” 83 Des Chene 1996: 138–156. 84 Hirai 2005: 481. Cf. Fisher 2006. LoLordo 2007. 85 Aucante 2006b. 86 Aucante 2006a: 303.

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Fig. 5.3 The movements of particles in the formation of animal (on the left) and vegetal bodies (on the right). In René Descartes, Primae Cogitationes circa generationem animalium, AT XI 534

spherical—that compose bodies. Such a distinction also arises in article 19 of the Fourth Part of the Principes de la philosophie, the French translation of the Principia. Here Descartes claims that “movements [. . .] must be circular when they occur along a single line, and spherical when they occur toward all sides of some surface” (Principes de la philosophie, IV, art. 19, AT IX-2210; MM 189). This is indeed what he claims in the note. The circular movement of particles occurs along a single line, while the movements of particles in animals occur toward all sides of a surface. Moreover, in the Principia, Descartes defined the second element, which is the most fluid among the three elements of his physics, as constituted by “spherical particles” (Principia philosophiae, III, art. 52, AT VIII-1105, 107, 148). These particles thus move spherically, while the more solid particles mostly move circularly. This differentiation between fluid particles moving spherically and solid particles moving circularly corresponds to the structural differentiation between seeds emerging in La Description du corps humain, where he proclaimed that the seed of plants is more solid than the seed of animals.87 The particles in plants have a solid structure and thus move circularly, whereas the particles of animal semen move spherically pursuant to their more fluid structure. However, Descartes’s description fails to provide a clear explanation of the difference between circular and spherical motions in this particular note. It is possible that this difference belongs to the mechanical degrees of freedom applied to living bodies, as discussed above, because Descartes also differentiates between the animals’ freedom of motion and the limitation of motion in plants. Their formation thus reflects their mechanical difference. Descartes then explained the movement of particles while composing plants. Accordingly, “particles of matter revolve from a to b and a, and from these other particles pass through from c.f towards d.e.c.g.h.f. of which [particles in] c f produce roots, d g [produce] branches and leaves, a b [produce] the trunk of the plant”

La Description du corps humain, IV, AT XI 253; G 186–187: “the seed [. . .] of plants, being hard and solid, can have its parts arranged and placed in a particular way which cannot be altered without making them useless. [The] seed in animals and humans is quite different, for this is quite fluid.” 87

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Fig. 5.4 The formation of plants. In René Descartes, Excerpta anatomica, Appendix, AT XI, unpaged, Fig. XXII

(Primae Cogitationes, AT XI 595 [translation is mine]).88 As it stands, this explanation is not particularly clear. Moreover, the image included in the text (see Fig. 5.3) does not square with Descartes’s description of the movement of particles and fails to clarify it. However, the edition of Descartes’s Œuvres by Adam-Tannery includes another image in the Appendix, which is the one reproduced in Leibnizs volume (see Fig. 5.4) and is much clearer.89 In this diagram, it is possible to see particles moving circularly from a to b. These particles form the trunk. At the same time, other particles move in circles from c to d e c and from f to g h f. When particles sediment in c and f, they constitute the roots; when they sediment in d and g, they form the branches and leaves. When enlarging the image (see Fig. 5.5), things look even clearer. Particles (the dots along the lines) move circularly from a to b and form the trunk or the stem of herbs, while in the other two circular motions, particles constitute the roots and branches. From a seed, particles start moving in these ways, forming trees by means of a combination of many circular motions. It is to be noted that in Descartes’s view, trees grow both upward toward the branches and downward toward the roots, as the movements of particles follow diverse directions. This description of movements reveals a direct observation of seeds (and plants), like those Descartes might have been performing with Reneri in 1638, therefore showing his aims at revealing a mechanical explanation of plant generation.90 A third and final issue of this note concerns heat. It is well known that heat is a source of life in Descartes’s physiology, as he proclaims in the Discours. Consistently with his mechanics, no difference arises between the heat in nature and the

Original Latin is: “partes materiae ex a volvantur versus b et a per illas transeunt aliae partes ex c.f versus d.e.c.g.h.f. quarum c f faciunt radices d g ramos et folia a b vero truncum plantae.” 89 See Aucante 2000: 169 n.39. 90 Aucante proposes that the fragments of Cogitationes were written in 1632/33, in Aucante 2000: 10, 53–55. Still, there is no evidence of this. I do not agree with this interpretation. 88

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Fig. 5.5 Author’s representation of the motions of particles, from Baldassarri 2019: 53

heat in living bodies.91 Yet, the reference to heat in this note importantly nuances this aspect. According to the Principia, heat generally operates in separating, purifying, consuming, and corrupting inert bodies, ejecting particles from them.92 Heat transforms inert bodies in different ways and agitates their particles.93 Generally, for Descartes, heat mainly works as a source of fermentation, as it changes the state of bodies from liquid to aerial, and makes their particles move, and fermentations play a role within bodily functions.94 In contrast, in this note Descartes describes a heat that operates in favoring the generation of bodies, rather than corrupting or consuming them. Similarly, in a note on the first page of the Primae Cogitationes, while describing the generation of bodies, Descartes claims that the force of the heat stimulates a simultaneous rush of particles together that activates life [efficient vitam].95 This issue recurs in the note of Excerpta anatomica, as the force of the heat makes particles combine in different ways, yielding life. This force of the heat bears a different result than the heat that separates and consumes bodies, suggesting a difference between the heat and fermentation in inert bodies and the heat endowing living beings. Such a differentiation seems corroborated by Descartes’s claim contained in a letter to Plempius of February 1638, when he stated that “in a few aspects, the heat of fire is dissimilar to the heat of the heart” (Descartes to Plempius, February 12, 1638, AT I 530 [translation is mine]). This entails a difference between living and inert bodies.

91 Discours, AT VI, 46. L’Homme, AT XI 201–202. Bitbol-Héspèries 1990. This issue was in stark contrast to Aristotelian tradition. 92 On natural heat corrupting bodies, see Principia, IV, art. 80–85, 92, AT VIII-1 249–252, 256. 93 For the transformation of bodies and agitation, see Principia, AT VIII-1218; 241. 94 On fermentation, see Bitbol-Hespériès 2016: 40. Schemechel 2022. 95 Primae Cogitationes, AT XI 505–506. Cf. Aucante 2000: 31.

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In sum, this note contains several issues. (1) Descartes compared animal and vegetal bodies as having similar living activities, namely generation. (2) He placed the explanation of the generation of living bodies within his mechanical framework, as he focused on the movement and arrangement of particles produced by the force of heat. (3) He posited a geometrical difference between the generation of plants and animals, following a difference between circular and spherical motions—consistent with his mechanical model. This distinction entails a mechanical differentiation between plants and animals, which notably corresponds to the diverse complexities of these bodies. (4) Finally, he specified that the force of heat activates life, distinguishing this heat from the one in nature and grounding a differentiation between the formation of inert bodies (see Sect. 4.4) and plant generation. While observing seeds and plants, Descartes thus developed a mechanical explanation of generation, consistent with his physics, ultimately showing a difference between plants and inert bodies, as well as a gradation between plant and animal generation.

5.3.2

Plant Nutrition and Growth

In a second set of notes, Descartes explains nutrition and growth in plants. The first note is the one entitled “On Accretion and Nutrition.”96 As we have already seen, in this text, Descartes differentiates between the accretion in inert bodies and nutrition in living bodies, revealing that an internal activity specifies the formation of different parts in plants and animals. In a second, large note, Descartes presents a theory of the formation of plants in their diverse parts, detailing the arrangement of particles. In Leibniz’s volume, this note on plants is collected in a section entitled Meteorologica, while AT does not report this division. For the moment, I focus on the first subsection of this note on fruit formation, AT XI 627–628 l.6, and on the third and fourth, 628 l.19–629 l.9 and 629 l.10–l.19. In the first subsection, Descartes writes: Fruits are formed in this way on trees: particles arise in a rectilinear motion from the trunk, which then turn back [and move] in circle, and there is another crosswise circular motion, through which the particles resulting from the mixture of these movements break more and more, and therefore the fruits ripen. (Excerpta anatomica, AT XI 627–628)97

In these lines, Descartes connects fructification to the movements of particles. Particles arise from the soil following a rectilinear movement within the little

96

Cf. Des Chene 2001: 133–138. Baldassarri 2018c. Original Latin is: “Poma ex arboribus ita formantur, emergent particulae ex trunco recto motu, quae deinde in orbem reflectuntur et fit alius motus circularis decussatim, cujus cum priori mistione particulae franguntur magis et magis, et ita fructus maturescit.” 97

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channels in the tree. Then, the particles start moving circularly.98 When the particles reach the branches, there is a mixture of circular movements. These motions make particles break and combine with other particles. As a result, these particles form fruits. Three things should be noted: (1) Descartes’s differentiation between motions, (2) the combination of different circular movements, and (3) the fragmentation and mixing of particles as the cause of the ripening of fruit. The first two are consistent with his physics, while the third is a new claim in Descartes’s philosophy of nature, although it is consistent with the note on Accretion and Nutrition examined above. In this description, Descartes stressed that a change made by the fragmentation and mixing of particles operates in nourishing the plant and producing fruit, similarly to nutrition occurring in animals. The third part of this note extends this explanation to the formation of plants in their entirety: Briefly said, all plants originate from the earth in this way: the force of the Sun makes abundant vapor rise from a part of the soil. Since the surrounding air resists the movement of this vapor, it makes some of the particles of the vapor dry out and arrange diagonally, while other particles rise rectilinearly in the fibers of the tree. Consequently, the bark has diagonal fibers, while the internal parts of plants have rectilinear ones. When some channels occur in the bark, the vapor moving between the bark and the wood and rising through these channels in an oblong manner takes a diagonal shape, thus forming the leaves. Instead, if while spreading through the marrow and the bark, the vapor moves between circular and diagonal fibers and takes a round shape, it then forms the knots of trees, then flowers and fruits, as shown above. In the middle of all plants, there is a cavity full of either vapor or marrow; since the particles of vapor do not rise rectilinearly, but sideways, moving from one part to another, as the fibers of wood tell us, [this sideways movement results in the fact that] the more solid particles move towards, [and compose,] the bark, [while] the lighter particles remain in the middle, as the Sun does among the planets. (Excerpta anatomica, AT XI 628–629 [translation is mine])99

This is a very dense and rather lengthy section, also containing some obscurities. First, Descartes inserted two references to the Sun, one at the beginning of this part and one at the end. The first reference is quite clear and a common topic in texts on plants at the time. As in Beeckman’s note, Descartes claimed that vapors rise within

98

On the relationship between rectilinear and circular movement, see Le Monde, AT XI 45. Original Latin is: “Summatim vero sic plantae omnes prodeunt ex terra: copiosus vapor vi solis per unam terrae partem ascendit, atque circumjacente aëre ejus motui resistente, partim siccatur, partim ejus fibrae, quae in rectum surgebant, in transversum volvuntur, unde fit cortex habens solum fibras transversas, cum e contra partes interiores habeant rectas. Si qui deinde meatus occurrant in cortice, vapor inter hunc et lignum ascendens per istos meatus oblongos solum in transversum eorum figuram sumit, et formatur in folia. Qui vero ex ipsa ligni medulla per lignum corticemque pervadit, quoniam inter fibras partim rotundas partim transversas egreditur, fit rotundus; atque ex eo concrescit primo oculus arboris, deinde flos, denique pomum, ut supra. Fit autem cavitas in medio omnium plantarum, vel aëre vel medulla plena; quoniam partes vaporis non plane recta sursum, sed oblique hinc et inde, ut patet ex fibris lignorum: quae ex iis sunt solidiores versus corticem feruntur, manetque in medio quod levius est, ut sol inter planetas.” 99

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plants due to the attraction of the Sun, similarly to evaporation. However, one should also note that, in a 1638 letter to Plemp, Descartes writes that there is an internal heat in plants that makes vapors move to the top.100 The second reference to the Sun is, instead, rather obscure. It presumably parallels the explanation of the formation of the heavens in Le Monde, where Descartes claims that some “matter of [. . .] heaven tends toward the outer surface of its heaven” (Le Monde, AT XI 109).101 Similarly, the lighter particles remain in the middle of plants and move within it, while the heavier particles are deposited in the external parts of plants. Second, Descartes focused on the movement of particles that rise from the earth in the form of vapors, which concur in nourishing the plant and producing its outcomes. Particles acquire different shapes while being disposed of within plants. When reaching the external part of the plant, particles dry and dispose diagonally. Otherwise, particles continue moving and reach the top of plants, forming branches, leaves, flowers, and fruits. Additionally, particles are arranged according to their different structures: The more solid constitute the bark. In this case, the particles of air resist the movement of the particles of plants and force the latter to dry out, sediment, and form the fibers of bark. No mixing between the air and the bark is possible, but the particles of the former operate on the second. The fibers of bark have a diagonal shape and a solid structure. In contrast, the fibers of the internal parts of plants have a rectilinear shape, for particles move from the bottom to the top of plants. In the middle of plants, however, there is a cavity or a channel with aerial particles (probably the vapor Descartes referred to) and the marrow. Since these vapors do not move completely rectilinearly from the bottom to the top, but sideways, as Descartes claims the fibers of wood make visible, these vapors carry all the particles from one part to the other. In this way, the particles disperse into different parts of the plant: Some particles reach the bark or enter its pores and constitute the leaves, and other particles remain within the plant and continue moving upward. What makes particles take a precise position is their structure: The heavier particles form the bark, the lighter particles constitute the pith. The latter particles move upward, change, and ultimately form flowers and fruits. At this point, Descartes seems to claim that the particles moving between the pith and the wood and the bark meet fibers that are round and diagonal. As particles move within these fibers, they acquire a round shape and constitute the eyes of trees, or knot holes, flowers, and fruits. Finally, in the last subsection of the note, Descartes differentiates between plants growing in the earth and growing underwater, consistently to his mechanical model. Accordingly, since plants underwater do not exhale vapors, because water surrounds the external pores of these plants, their structure is more porous than those growing

100

Descartes to Plempius, March 23, 1638, AT II 67. Cf. Le Monde AT XI 60: “the parts of matter [. . .] larger and more bulky [plus grosses et plus massives] soon had to take their course toward the outer circumference of the heaven. . .” 101

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on earth, and their particles have varied shapes.102 This is the only differentiation between plants in Descartes’s notes. Notwithstanding its complexities, this note reveals a sound mechanization of plants. Pursuant to the laws of motion, Descartes traced the ways in which the movement, disposition, shapes, and structure of particles form the different parts of plants, probably inferring this knowledge from the observation of the arrangement of particles. Taking advantage of the observation of vegetal bodies, Descartes thus explains the formation of plants in mechanical terms, ultimately confirming the mechanical model of his physics.

5.3.3

Grafting, Cultivating, and the Flavors of Plants

In a final set of notes, Descartes dealt with agricultural activities and some characteristics of plants and fruits that were the subject of contemporary botanical studies. The first case is an extract from the note previously analyzed: Grafting trees and spading and hoeing the soil cause the fruits to be more flavorful, because [in grafting] the particles carried throughout the pores of two trees of different genera change to a greater extent. Likewise, when the soil is frequently hoed, the subtlest particles are attracted; for if the soil remains in the same place for a long time, its little particles gradually come together in the same part to such an extent that the roots of trees become similar. Moreover, if the soil is often hoed, then particles enter in trees in one way, other particles in other ways, and there they mix better. Indeed, dissimilar things need to break into more parts in order to mix. For this reason, fruits from wild trees are unripe. (Excerpta anatomica AT XI 628)103

Several issues arise. The first thing to note is that an internal change in particles is necessary to constitute the parts of plants and, especially, to produce fruit. This is consistent with Descartes’s interpretation of nutrition and bodily formation as the change, fragmentation, and mixture of particles analyzed in the previous notes, when the more solid particles form the bark, and the more fluid form the pith. The second issue concerns the connection of these results with two agricultural activities: grafting and hoeing. Descartes describes the ways these activities make the particles change within the body. Ultimately, a mechanical explanation underlies this issue, as the more these particles change, the more fruits become flavorful.

102

Excerpta anatomica, AT XI 629. See Roos 2007: 80–83. Original Latin is: “Insitio vero vel etiam solius terrae cultura faciunt ut fructus sint mitiores: quia nempe particulae per duarum diversi generis arborum meatus evectae magis interpolantur. Item ex terra saepius versa subtiliores partes attrahuntur: quia, si terra diu resederit in eodem loco, paulatim ejus minutiae in easdem partes conspirabunt, adeo ut radices arborum similes sint iturae; glebis autem saepe versis, contra una arborem ingredietur uno modo, alia alio, meliusque ibi miscebuntur; dissimilia enim, ut misceantur, debent in plures partes frangi. Hinc fructus omnes sylvestres fiunt acerbi.” 103

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In the early seventeenth century, grafting received varied attention. Both Aristotelian commentators and alchemists considered grafting as performing a transmutation of vegetal species.104 Natural philosophers such as Della Porta considered grafting a form of copulation between bodies. Botanists such as Bartolomeo Taegio (1520–1573) claimed grafting was an industry constructing a third nature and producing more flavorful fruits.105 In Sylva Sylvarum, Bacon ceased to claim grafting as a model of copulation between plants and considered it a kind of nourishment.106 Descartes was not interested in the idea of producing new species or new fruits, nor did he connect grafting to surgery.107 In contrast, he appears to be aware of Bacon’s interpretation and proclaims grafting favors the nourishment of plants, as it renders the movement and mixing of particles easier. Since grafting makes particles change the more, grafted plants produce flavorful fruits. It is to be noted that Descartes wrote of trees of different kinds or genera, while botanists generally claimed that grafting with trees of the same genre was possible, and sometimes a better solution. In the case of hoeing, Descartes related this technique to the internal change particles undergo when entering the plant and forming its parts. The more particles are broken and changed due to hoeing, the more they enter the roots in different ways, the more they easily mix within the body of plants, and the better the fruit is. When these activities are missing, the fruits are unripe or sour, a quality he describes in another text, entitled De Saporibus [Of Flavours].108 In another note, Descartes discussed pruning: Several trees have been found underground in Holland all turned upside down in order to make the branches look towards the North. If one wants to have tall trees, one should not cut suckers, because many others would sprout, but instead [one] should overturn and bind the branches to the trunk, so that they will die.As long as one plants new trees, it is necessary to prune their branches and roots: the roots in a way that makes their fibers touch the largest amount of ground, so that new roots develop and stick more firmly in the soil. (Excerpta anatomica, AT XI 626 [translation is mine]).109

104

Newman 2005: 65–66. On grafting, see Savoia 2017. 106 On Bacon’s experiments, see Rusu and Lüthy 2017. 107 When Mersenne asked Descartes about the plant growing on the body of a Spaniard, Descartes’s answer focuses on the affinity between plant and animal bodies, claiming that the same principle of life makes them alive. Plants grow on human bodies for this reason. He did not refer to grafting nor to surgery. Descartes to Mersenne, July 30, 1640, AT III 122. 108 De Saporibus, AT XI 541. 109 Original Latin is: “Arbores infra terram inventae sunt in Hollandia omnes ita inversae sunt, ut rami septentrionem respiciant. Si arbores proceras habere vis, ne reseca surculos, plures enim renascerentur; sed eversos trunco alliga, ita enim emorientur. Dum plantantur novae arbores, rami et radices abscindi debent; radices autem ita ut fibrae quam maxime terrae insistant; ita enim firmius inhaerentes, novas radices agunt.” 105

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Let us analyze this note sentence by sentence. In the first line, Descartes refers to some trees found underground in Holland, a region of the Dutch Republic that includes Leiden, Santpoort, Alkmaar, the towns where Descartes lived from 1637. Although it is impossible to claim whether this is Descartes’s own observation or belongs to a sentence he copied from elsewhere, it is possible that this experience occurred near to him, and so it is possible to date it after 1637. Although it is not clear what he means by trees growing underground with the branches directed toward the North, this phenomenon has various interpretations. Medieval chronicles reported that the beginning of Dutch Christianisation was accompanied by a fall of trees, which then began growing horizontally underground.110 Inverted trees (as trees growing underground may indicate) were a mythological and mystic symbol that characterized hermetic traditions. In Renaissance Platonism, inverted trees pointed to magic, obscure knowledge and were related to Rosicrucianism (a sect combining mysticism, hermetism, alchemy, to which Descartes was sympathetic in his youth).111 Still, the folkloristic, historical, and mystical interpretations of trees growing underground are far from Descartes’s interest. Apparently, Descartes extracted this discovery and embedded the phenomenon within his mechanical explanation of plants. He relates these trees to his explanation of the particles moving within them. Binding the branches toward the North, where the Sun does not hit them, helps trees grow taller. Branches do not grow, because the Sun does not attract sap in their direction, and all particles thus proceed to the top of the trees. This mechanics of plant growth has been discussed earlier. Next, Descartes acknowledges the importance of cutting, or pruning, and binding branches to the trunk. He includes root pruning, as this activity makes the roots stick more firmly in the soil. In this way, more particles could enter the roots and nourish the tree, and new roots develop. In all these cases, the trees grow healthy and fruitful. This note reveals Descartes’s knowledge of agricultural activities, as he focuses on the ways of producing more flavorful fruits or taller plants. The last note I am going to examine develops from the possibility of extracting salt from water, a topic in Les Météores examined in Sect. 4.3.2, from which Descartes moved to investigating the presence of salt in vegetal bodies: There are no salty fruits that I know of, and this sufficiently proves that salt is quite fixed, and that the Sun does not make salt grow in plants. [. . .] Several fruits are bitter, in particular those growing in hot regions, like the shells of nuts, oranges [malorum aureorum], and so on. Bitter things usually purge quite violently and dry up, and even irritate and sever the extremities of veins. From this I deduce that heat initially stirs up several particles of smoky vapor that are shaded and black (as in the shell of nuts), so that afterwards these particles are gradually secreted by the rapid movements of fluid particles in the tree, and simultaneously pressed together: thus, the more olives ripen, the more bitter they are. As a result, these particles compose a very thick and wet body, which

110 On trees growing underground as the origin of Dutch civilization, see the terms “Batavia,” in Hofmann, Lexicon Universale: 261. Cf. Bejczy 1991: 83. 111 Gouhier 1958. Shea 1988.

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with respect to human flesh is dry, and so this body purges our limbs; for in fact, what is very thick clings to the humors, and this thick body carries everything with itself with the exception of the most fluid parts that are left to heat up and dry [the human body]. (Excerpta anatomica, AT XI 622–623 [translation is mine])112

In this note, Descartes expanded his study of the structure and formation of fruits. First, he claimed that fruits are not salty, because salt does not grow in plants, nor does the Sun elevate salt within plants. Despite the early modern debate concerning the presence or the preformation of salt in plants that attracted chymists and naturalists, Descartes appears reluctant to join this discussion.113 For instance, in the Principia, he claimed that only “sweet or insipid waters [. . .] are distilled from plants” (Principia philosophiae, IV, art. 120, AT VIII-1268 [translation is mine]). By means of distillation, he confirms his theory that salt neither runs within the channels of plants nor dwells in the solid structure of plants. Descartes then explains what produces the flavor of fruits. He challenges the idea that flavor and taste are due to qualities such as hot or cold and explains them in the mechanical terms of his physics.114 In this case, flavor depends on the movement of vapors and particles within plants, which are arranged in determinate ways while composing fruits, as previously seen. In this note, he especially deals with bitter fruits. He starts by claiming that bitter fruits grow in hot regions, as the cases of nuts and oranges reveal.115 He then claims that bitter fruits purge human bodies as they dry and irritate them, or even sever the extremities of veins. Since smoke causes similar effects on living bodies, Descartes infers that smoky vapors compose bitter fruits. In hot regions, the Sun rises hot and smoky vapors, which enter into the composition of fruits. As a result, bitter fruits grow in hot regions. Descartes then describes the internal composition of these fruits as he details the movement of particles within them. The most fluid particles in plants push and press these smoky particles together. These fluid particles then compose a thick wet body. Presumably, this body is the fruit itself. Descartes is probably writing of oranges, whose internal part is juicy, or olives, to which he refers in the note. Although the note is not very clear, Descartes seems to imply that some smoky vapors remain among the fluid particles of sap and take part in composing the fruit. These vapors make the fruits bitter. In this sense, flavors depend on the disposition of particles Original Latin is: “Nulli quod sciam fructus salsi proveniunt: quae satis indicant sal esse valde fixum, nec a sole in plantas elevari. [. . .] Amari sunt plerique fructus, ii praecipue qui in calidiusculis regionibus nascuntur, ut nucum putamina, malorum aureorum, etc. Abstergunt autem amara omnia vehementissime et exsiccant; imo etiam exulcerant, et venarum extremitates resecant. Ideo concludo esse partes in fumum quidem ab initio a calore excitatas, ideoque opacas et nigras (ut in nucis cortice), postea vero in arbore a partibus fluidis celeriter motis paulatim secretas et simul constipatas (unde olivae, quo maturiores, eo magis amarae), ac proinde quae faciunt corpus humidum crassissimum, quod se toto respectu carnis nostrae est siccum, ideoque abstergit; illi enim quod crassissimum est, in humoribus adhaeret, et sic omnia secum vehit, fluidissimis exceptis, quae relicta calefaciunt et siccant.” 113 See Roos 2007: 85–96. Clericuzio 2018. 114 See Roos 2007: 15. 115 On oranges (aureorum malorum) see Ferrari, Hesperides. Cf. Baldassarri 2022c: 278–279. 112

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according to Descartes: In sour fruits, flavor depends on unmixed or unchanged particles, while in bitter fruits the flavor depends on the presence of smoky particles that rise from the soil to the top of trees. The mechanical change and disposition of particles compose fruits and operate in defining qualities such as the flavor of fruits. As a result, Descartes explains that the disposition of particles makes fruits harmful or beneficial to human beings in a way that is consistent not only with his own physics, physiology, and medicine but also with his metaphysics.116 In this case, due to the presence of smoky particles, bitter fruits will dry, heat, and irritate the human body, even though they may be juicy and composed of a thick, wet body. This note on the formation of fruits adds something to Descartes’s theory of sensation and to his physiological explanation of harmful or nourishing bodies. According to this theory, if food tastes bad it is harmful. While in L’Homme Descartes only explained taste from a physiological analysis of the nervous system, in this note, he describes the role played by the disposition of particles in fruits that produce their taste. Thus, he reveals what makes bitter fruits harmful, namely the mechanical arrangement of particles and the presence of smoky particles, making this note preparatory to his study of therapies.

5.4

Conclusion

Although there is no section on plants in Descartes’s natural philosophical text, his correspondence and several notes collected in Excerpta anatomica reveal the role of his botanical observations and experimentation as a compelling section of his work. Still, problems remain. The first is the absence of a clear definition of plants, as Descartes’s interpretation oscillates between his early claim of plants as inert bodies—as both grow by acquiring matter from outside—and his later bracketing of plants with animals as living bodies, although he specified several mechanical differences between them. The second is the exact subject he should investigate in the study of plants, something he voiced in article 188 of the Principia. Throughout the years, Descartes tried to reduce the study of plants to a section of animals—this especially surfaces in his attempts to isolate an internal principle of plant life and vegetation—but significant differences arose, revealing the necessity to deal with plants in their own right. Indeed, although plants represent a clear case of hydraulic machines, therefore consistent with Descartes’s analogy of the animal-machine, he felt compelled to investigate how much his mechanical physics applied to this field, finding that he could not entirely apply the physiological framework he used for animals. The third problem is to evaluate the extent of his work with plants, as his notes are not always dated; as they stand, it is likely that he significantly worked on plants from late 1637 for several years, but this is not utterly certain. Different from

116 On harmful and beneficial, see Meditationes de prima philosophia, VI, AT VII 74, 81, 83, 88–89.

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the case of rocks and minerals, examined in Chap. 4, historians only possess Descartes’s correspondence and several notes, in which his focus on the observation of the mechanical structure of plants, the (geometrical) movements, change, shape, and disposition of particles that compose plants and activate their living functions importantly reveals his experimentation with vegetal bodies and shapes his mechanization of plants. In this chapter, I have dealt with these issues. I have highlighted the changing definition of plants, from the early 1630s to the years after the publication of the Discours. The turning point apparently developed as Descartes started investigating nutrition in 1637, as he differentiated living bodies’ nutrition from inert bodies’ accretion and provided plants with a vegetative power. However, despite the fact that his mechanical framework reduced bodily diversification, differences between animals and plants do emerge. For instance, due to their less complex physiological and organic structure, plants do not display sensation, despite his theoretical claim that the sensitive herb should reveal the presence of similar organs in plants and animals. As a result, Descartes’s studies of plants mostly focus on the vegetative activities, namely generation from seeds, nutrition, growth, and fructification, as vegetation and vegetative overlap in his investigation. A significant part of his understanding of plants was apparently spurred by his experimental collaboration with Reneri, and he probably profited from his friendship with the director of the Leiden botanical garden and other fellows interested in the corpuscular structure of plants, although Descartes did not take full advantage of the Dutch attraction for specimens, singularities and rarities, or particular effects—he rejected catalogs as a collection of names and distanced himself from Baconian curious experimentation that gained momentum in seventeenth-century Dutch culture. In contrast to the Baconian exploration of new effects, Descartes mostly performed experimentation to understand the causes of plant life, observing how much his mechanical physics operated in a specific field as he investigated the movement of particles throughout the generation from seeds, plant nutrition, growth, and fructification. As he explained plant activities through his mechanical physics, he anticipated some features of the botanical knowledge of the second half of the seventeenth century. At the same time, Descartes examined some vegetal phenomena that were widely discussed in his context, such as vegetal sensation, tree growth underwater or underground, fructification, and agricultural techniques (such as grafting, hoeing, and spading), providing a mechanical explanation for all of these cases and ultimately mechanizing fruits (such as citrus). This part was not unrelated to his explanation of taste and his attempt to provide a series of vegetal therapies for the human body. In sum, his study of plants appears consistent with his philosophy and physics, namely with his theory of vortices, his study of light, his rules of motion, and his definition of nature as extended matter, which are the principles of his explanation of plant life.117 In using plants to probe more deeply into the basic functions of life—

117

Principia philosophiae, IV, art. 187, AT VIII-1 314–315.

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i.e., generation and nutrition—from a mechanical perspective, Descartes shed important new light on several underspecified features of his early physiology, developing the notion of an internal vegetative power activating life, the immutatio, thus making vegetal physiology a compelling field of his study of living nature and the animal body. As a result, he bridged the gap between plants and animals, ultimately providing a mechanical difference between plants and inert bodies. While neither taxonomies, classifications, nor the botanical enthusiasm of his contemporaries attracted his philosophical attention, Descartes’s botanical endeavor restricts his investigation to the geometrico-mechanical movement and arrangement of particles in plants, and this mechanization of vegetable life brings to light a section of plants utterly consistent with his philosophical program.

Chapter 6

Animals

Abstract Despite the efficacy of Descartes’s animal-machine analogy, a crucial issue affects his mechanization of animal bodies. This reduction works for the animal in general, that is an abstract representation of the animal body, while the higher functions and behaviors of animals (and men) in particular cannot be entirely mechanized. In this chapter, I tackle this asymmetry, showing that Descartes used the analogy with machines as a heuristic model to explain living functions but stopped the analogy when necessary to expound animals as a system or to illustrate life. This especially surfaces as he focused on particular animals, as a sort of scale of bodies emerges in his biomedical manuscripts. In the last section of this chapter, I disclose Descartes’s exploration of animals as a coherent organic unity of functions, as his study of particular bodies allowed him to produce a more complex investigation of animal beings, which, however, retained plenty of puzzles.

Together with plants, a study of animals in their own right is nowhere to be found in Principia philosophiae,1 yet the animal body significantly populates Descartes’s texts at large. His attention to living natures is principally built on the study of the physiology of animals, a crucial aspect of his medicine.2 Yet, while performing a mechanical reduction of the functioning of organs, Descartes claimed he had dealt with “the animal in general” (Descartes to Mersenne, February 20, 1639, AT II 526) as he wrote to Mersenne in 1639, and not with the man in particular. Albeit Descartes is here speaking of medicine and therapeutics, this passage reveals a broader challenge concerning his study of living bodies. In his work, Descartes had focused on the anatomical study of the animal in general, avoiding any particular cases, as in following his geometrico-mechanical model he reduced the animal body to a machine. Accordingly, the better way to know the animal’s functions is to deprive it of any singular, particular characteristics. This description suits his program but 1

See Principia philosophiae, IV, art. 188, AT VIII-1 315. Plemp’s report of Descartes immersed in meditations and anatomical dissections is well known. See Plempius, Fundamenta Medicinae: 375–376. Cf. Descartes to Mersenne November 13, 1639, AT II 621. 2

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 F. Baldassarri, René Descartes’s Natural Philosophy and Particular Bodies, Studies in History and Philosophy of Science 60, https://doi.org/10.1007/978-3-031-48663-0_6

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reveals a very abstract perspective. And bridging the gaps between the studies of the animal in general with animals in particular unearths a problem—something similar occurs in his medicine.3 As for the case of plants, the main issue is that the geometrico-mechanical model seems to be insufficient to describe animals in their own right or to deal with animal bodies in particular.4 A discrepancy develops. On the one hand, Descartes claimed he could explain animals in the same way he explained “[the formation] of a grain of salt or of a little star of snow in [the] Météores” (Descartes to Mersenne, February 20, 1639, AT II 525 [translation is mine]), namely through his mechanical reduction of nature to a few mechanical laws of motion and “in terms of the properties of fundamental particles” (Theurer 2013: 913).5 In taking the reduction of animals to machines as literarily as possible, following the identity between nature and mechanics, Descartes explained living activities through describing the interaction of particles that we found in his study of minerals and rocks, and in some cases in those of plants. In this sense, a study of animals is utterly consistent with his metaphysics and physics. On the other hand, since animals reveal a systemic organization that eclipses any reduction to corpuscles, he recognized that animals are more complex than machines and automata, and studying animals in particular reveals several differences and behaviors that should be accounted for in his program.6 Combining the abstract idea of animals as machines with the particular cases is, however, problematic, while the reduction of animals to automata fails to apply entirely— ultimately revealing a gap between his physics and his physiology of living beings. Recently, interpreters have challenged the universality of the animal-machine identification, according to which Descartes had merely deprived animals of several processes connected to life, namely passions, and cognition, ultimately reducing them to automata. Against this line, Gaukroger has significantly claimed that the reduction of the study of animals to the doctrine of the animal-machine “has been widely misunderstood, above all because it has been construed as eliminating any sentient and cognitive states in animals, whereas, in fact, not only does Descartes not deny such states to animals, his mechanist account is designed to offer an explanation of such states” (Gaukroger 2002: 181). While Descartes appeared interested in explaining animal behaviors, making these consistent with his reduction of animals to statues, namely to things without any behavior but just a mechanical set of motions, appears problematic, as these features cannot be entirely reduced to his mechanical physiology.

3

On the failures of Descartes’s medicine, see Guéroult 1985: 198–201. Cf. Aucante 2006a; Baldassarri 2021a; Baldassarri 2023a; Verbeek 2023. 4 Problems in defining animals characterized the early modern period. See Begley 2022. 5 See also Hatfield 1992; Hatfield 2000; Bonicalzi 2006. 6 See Discours de la Méthode, V, AT VI 56; CSM I 139: “they will regard this body as a machine which, having been made by the hands of God, is incomparably better ordered than any machine that can be devised by man, and contains in itself movements more wonderful than those in any such machine.”

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This does not entail that Descartes rejected the mechanical reduction of animals altogether. As pointed out by Barnaby Hutchins, in physiology, Descartes is not “a strict explanatory reductionist [. . .] but [he stops] the reduction where appropriate” (Hutchins 2015: 687). In discussing singular functions, Descartes appropriately applied his mechanical framework, a fitting explanatory tool; therefore, the analogy between animals and machines appears as a model for explaining the functioning of bodies in a clear physiological and physical framework, consistent with the laws of nature and his theory of matter.7 Still, as Dennis Des Chene has made clear, there is more than the simple reduction of animal bodies to corpuscles in Descartes, and as Deborah Brown has revealed, an interdependence of systems surfaces in Descartes’s study of animal bodies.8 Both an interconnection of functions and the interpretation of living bodies as a systemic organization make Descartes’s interpretation proceed beyond the mere mechanistic reduction and ultimately lays bare the complexities of the study of animals in particular. Evidence of this asymmetry surfaces in Descartes’s texts. For instance, in the last section of La Description du corps humain, Descartes suggests the importance of knowing the interaction of corpuscles in the formation of the fetus: Now since the solid parts of the tiny filaments are composed, turned, folded, and intertwined in various ways, following the various routes of fluid and fine matters [. . .] and following the shapes of the places [. . .], if one had a good knowledge of all the parts of the seed of some species of a particular animal [. . .] one could deduce from this alone, by entirely certain and mathematical arguments, every shape and structure of each its bodily parts. [. . .] But because I am considering only the production of the animal in general here, and to the extent that there is no need to explain how all its parts are formed [. . .], I shall continue just to explain the formation of the principal bodily parts. (Description du corps humain, V, AT XI 276-277; G 200 [emphasis is mine])

Accordingly, by studying the motions and arrangements of particles, one may deduce the formation of animals by mathematical reasoning, that is, from a geometrico-mechanical perspective, consistent with the principles of his philosophy. Yet, by these means, he had only been able to explain the formation of the principal parts of the animal in general, as if he was reconstructing a model, while he could not expound particular bodies. This entails that his corpuscular-mechanical explanation works up to the point of reconstructing the living body as a machine, that is, by dealing with its structure and activities taken in themselves, and in this sense, Descartes discussed a general, abstract model, while a study of specific, individual bodies avoids this framework. In L’Homme, he dealt with the animal body as a statue, a mere aggregation of diverse machines. Yet, something else surfaces, as he also assumed the circulation of blood as a connecting function, the point of departure for the reconstruction of the physiological activities of the animal body and of its formation, but also a uniting 7

Both in L’Homme and in La Description du corps humain, a study of the mechanical movement of particles buttresses Descarters’s explanation of several functions of living bodies. See Chap. 5 of this book for the case of generation. 8 Des Chene 2001. Brown 2011.

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principle. In this sense, animals are not just a combination of particles, but living creatures with an internal activity and coherence. Nonetheless, at this stage, he did not take this point to its philosophical consequence. While in the case of minerals and rocks there is an identity between the explanation of general and individual bodies, this identification does not easily apply to animals. Two levels develop in the latter case. The one is the mechanical explanation of the basic processes in themselves. The second is the explanation of animals as systems performing self-motions, self-arrangements, and being equipped with sensation, imagination, and emotions, a set of actions that specifies individual behavior and cannot be found in inert bodies or in automata. The latter point cannot be easily reduced to a mechanical pattern. The study of parts of the body concentrates on the mechanical functioning of the organs which are united in a statue, as in clocks. But animals reveal another kind of complexity, which pertains to their system or unity, whose principle is an internal activity. While discussing this internal activity in plants produced the definition of the immutatio, that is, a vegetative power, in the case of animals, the definition of an internal principle cannot be restricted to nutrition. Another example of such a discrepancy can be found in his famous discussion of the heat within the heart. While in the Discours he had reduced the heat in the heart to a natural one, and had described its functioning in the mechanical terms of particles moving and performing precise activities, in the correspondence with Plemp he acknowledged a difference between these two heats, and he investigated some particular cases, revealing a gradation between heats. While the mechanical framework persists, insofar as Descartes clearly rejected any appeals to matter qualities or nonmaterial principles regulating living bodies and encompassed physiology within a mechanical reduction to corpuscles that work for the study of minerals as well as for animals, his mechanization of the animal world is more nuanced than expected, and animals appear not just as mere machines—and not just because he owned a little dog, named Monsieur Grat.9 This discrepancy follows Descartes’s goals. In isolating singular organs for a physiological investigation, Descartes followed a mechanical reduction, making the animal-machine a heuristic model to explain the physiology of organs, but as he dealt with the living bodies qua living, i.e., displaying complex behavior, he ignored the reduction and investigated the body as a unity or system of activities. While this point did not entirely surface in his work on plants, this is much clearer in his study of animals in their own right. In the first section of this chapter, I concentrate on the study of animals as automata, restricting this model to a mechanical framework which serves for the physiological study of the singular parts. Yet, despite this mechanical framework, Descartes endowed animals with sentient states, emotions, memories, and complex behaviors that do not entirely fit his mechanization. While trying to explain these

9

On this story, see Baillet, La vie de Monsieur Descartes: II 456, in margine of a letter from Descartes to Picot, February 28, 1648, AT V 132–133.

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features within his framework, the animal-machine model helps illustrate the origin of the animal activities but cannot work in devising the whole picture of animal behavior. In the second section of this chapter, I unearth Descartes’s efforts to deal with particular, existing cases, which disclose animal activities—such as instincts— as an important subject for Descartes’s interpretation of animals.10 In the third section, I focus on his study of particular animal bodies collected in his biomedical manuscripts, where a sort-of mechanical hierarchy from oysters and sponges to birds, fish, sheep, calves, dogs, and brutes ultimately surfaces. This gradation, however, resides in the investigation of bodies as systems, while in isolating the singular functions, the physiology of the diverse animals helps the philosopher to shed light on the singular functions of the human body. Conceiving animals as a system of actions blurs the boundaries between brutes and humans, whose only difference resides in the presence of the rational soul.11 Finally, I deal with Descartes’s attempt to conceive the animal body as a coherent unity, or an interdependence of activities, which grounds the understanding of living bodies as an organic system and not as mere automata. While Descartes’s mechanical reduction specifically operates to ground a physiology of living bodies, the interdependence of living functions, animal behaviors, and life as an organic unity forgo this framework, making Descartes’s study of animals a complex enterprise that proceeds beyond his philosophical program.

6.1

Automata and Animal Bodies

A few decades ago, John Cottingham dealt brilliantly with the “monstrous view [that] commentators attribute to [Descartes]” (Cottingham 1978: 551),12 namely that animals are nothing but machines. In breaking down Descartes’s “vague and ambiguous” doctrine, Cottingham reveals a more complex condition of animal life in Cartesian texts. More recently, Peter Harrison and Gary Hatfield have discussed this issue thoroughly, showing that a more nuanced interpretation of animals outlines Descartes’s philosophy of nature.13 Yet, Descartes’s study of the living body develops from the implicit claim that the animal body is a machine. At the beginning of L’Homme, Descartes indeed writes that he has supposed “the body to be just a statue or a machine made of earth,” which is made by pieces. Since such a statue could “imitate all those functions we have”

10

See also Kekedi 2015. On the difficulties in dividing animals and humans in the Renaissance and early modern period, see Buchenau and Lo Presti 2017. 12 See also Vartanian 1953. Descartes’s interpretation shaped the seventeenth-century interpretation of animal bodies, see Sharp 2011; Riskin 2016: 70. 13 Cf. Harrison 1992. Hatfield 2008. For an alternative interpretation, see Newman 2001. Thomas 2020. 11

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(L’Homme, AT XI 120; G 99), Descartes inferred that these could be thus explained from his matter theory and from the sole disposition of organs. Then, he continued with the claim that self-moving machines such as fountains, mills, and clocks help him suppose that the living body is a machine made by God. However, in the Fifth part of the Discours, Descartes argues that despite the comparison of automata constructed by men with actual living bodies made by God, a difference surfaces in the multitude of little parts within animals, for “having been made by the hands of God, [a living body] is incomparably better ordered than any machine that can be devised by man, and contains in itself movements more wonderful than those in any such machine” (Discours de la Méthode, V, AT VI 56; CSM I 139). Although this metaphysical–physical distinction is meaningful, Descartes does not explore the issue further. He continues stressing that, in principle, no differences between a machine and an animal surface: “if any such machines had the organs and outward shape of a monkey or of some other animal that lacks reason, we should have no means of knowing that they did not possess entirely the same nature as these animals” (Discours de la Méthode, V, AT VI 56; CSM I 139). While Descartes raises this argument to show where the difference between animals and humans lies, if we stop our reading in the lines just quoted, he appears to be asserting that animals and machines are identical. Despite such a claim, Descartes did not commit to the thesis that animals are mere automatic bodies. Two reasons help confirm this point. The first consists of understanding Descartes’s physiological aim. In the section of the Discours where he introduced his physiology of the living body, Descartes elaborated the animalmachine comparison as a helpful methodical tool to ground his medicine in his physics. This is somehow confirmed in La Description du corps humain, where he stresses that “the ignorance of anatomy and mechanics has contributed to [the ignorance of medicine]” (La Description du corps humain, AT XI 224; G 170). The animal-machine comparison serves to dismantle the curious attractions to machineries and esoteric projects of constructing living bodies and reveals a theory to frame the organization of processes.14 As a result, this is an explanatory way to medical knowledge, which, however, does not result in an ontological definition of animals as machines.15 This leads to the second issue. As the text of L’Homme clearly reveals, Descartes’s mechanical physiology primarily works for the understanding of human nature. This stretches the comparison to include men within the animal reign and ultimately extends the analogy with automata. As a consequence, humans are like machines, and all their functions, including life, belong to machines—yet, how much life could be accounted for in the mechanical terms of his framework remains obscure.16

14 Cf. Rodis-Lewis 1956. Macdonald 2002. Bonicalzi 1987. Marcialis 2011. For a more recent survey of mechanism and living bodies, see Bertoloni Meli 2019. 15 Cf. Manning 2013. 16 I have reconstructed these problems in Baldassarri 2021d.

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An attempt to specify a principle of life surfaces at the end of L’Homme, where he outlines that “to explain these functions, then, it is not necessary to conceive of any vegetative or sensitive soul, or any other principle of movement or life, other than its blood and its spirits which are agitated by the heat of the fire that burns continuously in its heart, and which is of the same nature as those fires that occur in inanimate bodies” (L’Homme, AT XI 202; G 169). In rejecting the system of souls as a principle of living functions, Descartes reduces animal activities to the arrangement, disposition, and movement of particles, that is, to his mechanical physics, through which he claims to have been able to explain all the functions attributed to the machine, ranging from the digestion of food to sensation, imagination, memory, and passions, as he did for inert bodies. Yet, the fact that the animal-machine possesses higher faculties, outstandingly lets a tension surface, as these cannot be easily reduced to his mechanization—and this concerns life too. Consequently, the animal-machine analogy should stop at this point, for the higher functions (and life) can only partially be mechanically expounded.17 The question is how far sensation and passions pertain to the body, and therefore to the mechanical organization of them. In the Discours, Descartes claims that animals (or machines) differ from men in the fact that they do not think—“they were acting not through understanding but only from the disposition of their organs” (Discours de la Méthode, V, AT VI 57; CSM I 140). This entails that animals have no rational soul, or res cogitans, that in Descartes’s philosophy means no soul at all, but does not entail that animals are insensible or unpassionate machines. In summarizing the work of L’Homme, Descartes stresses to have been able to explain sensation, emotions, memory, and fantasies within the mechanical framework of his physiology and without any appeal to the rational soul.18 Although L’Homme concerns human nature, in providing a physiology of sensation and emotions in the mechanical terms of his physics, the text develops the animalmachine model, ultimately resulting in an explanation that concerns both animal and human bodies. Insofar as these operations are in the machine, animals are entitled to have sensation, feelings, exactly as they occur in the human body. Still, since sensory experience is not detached from a cognitive structure, animals are entitled to have one, although they lack self-consciousness, that is, the knowledge to see, to feel and so on, as this pertains to the mind—and thus to human beings alone. In the Discours, Descartes describes this difference through two features: First, animals lack the elaboration of thoughts through a language, and second they have perfect skills in performing specific operations but lack the ability to do things that require reasoning, that is, learning to do something and solve problems.19 Still, he 17

Gaukroger has claimed that a sort of psycho-physiology develops in the study of animals too, see Gaukroger 2002: 196–214. 18 Discours de la Méthode, V, AT VI 55. On memory in brutes, see Regulae ad directionem ingenii, XII, AT X 416. 19 One should note that Descartes buttressed his claim by means of the example of the dull-witted and madmen. Cf. Discours de la Méthode, V, AT VI 57. See Descartes to Reneri for Pollot, April or May 1638, AT II 38–41.

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stops this reflection at this point and only claims that one should avoid “imagining that the souls of the beasts are of the same nature as ours” (Discours de la Méthode, V, AT VI 59; CMS I 141). This is important, as one must rid oneself of the inveterate prejudice that “brute animals [. . .] have feelings like us” (Descartes to Mersenne, July 30, 1640, AT III 121; CSMK 149), but this does not entail that they do not have sensation. Yet, a more precise investigation of the higher functions in animals did develop but only at a later moment. It is only in his 1640s correspondence with Cavendish and Henry More (1614–1687) that Descartes refined his interpretation of animal behavior. This, however, contains a problem. Despite confirming that all animal movements “originate from the corporeal and mechanical principle,” and that “the astuteness and cunning of dogs and foxes, or by all the things which animals do for the sake of food, sex and fear” can be “easily explain[ed] as originating from the structure of their bodily parts,” he then added something important. Accordingly, it cannot “be proved that there is no [thought in animals,] since the human mind does not reach into their hearts” (Descartes to More, February 5, 1649, AT V 276; CSMK 365). What one could claim is that “since [animals] have eyes, ears, tongues and other sense-organs like ours, it seems probable that they have sensation like us; and since thought is included in our mode of sensation, similar thought seems to be attributable to them” (Descartes to More, February 5, 1649, AT V 278; CSMK 366). This point challenges his mind–body dualism in a way that is connected to his study of passions, something he was elaborating at the time. Accordingly, some animals like “horses and dogs [. . .] learn what they are taught [. . .]; and all animals easily communicate to us, by voice or bodily movement, their natural impulses of anger, fear, hunger, and so on,” which, however, “depends on a bodily organ” (Descartes to More, February 5, 1649, AT V 278; CSMK 366). A similar issue surfaces in his correspondence with Cavendish. While he rejects Montaigne and Charron’s claims of the superiority of animals,20 Descartes discusses instincts. For instance, magpies could: say good-day to [their] mistress when seeing [them] approach [. . .]. It will be an expression of the hope of eating, if it has always been given a titbit when it says it. Similarly, all the things which dogs, horses and monkey are taught to perform are only expressions of their fear, their hope or their joy, and consequently they can be performed without any thought.” (Descartes to Newcastle, November 23, 1646, AT IV 574–575; CSMK 303 [emphasis added])

Moreover, thanks to instincts, “animals do many things better than [humans] do,” as one could draw from this that they “act naturally and mechanically, like a clock which tells the time better than our judgement does” (Descartes to Newcastle, November 23, 1646, AT IV 575; CSMK 304). Descartes listed the activities of honeybees, the flight of swallows and cranes, apes in fighting, or the instincts of dogs and cats, as evidences of such a perfect set of animal operations. Still a crucial

20

See Gontier 1998: 184–196.

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difference arose, as Descartes concluded that “they act only by instinct and without thinking” (Descartes to Newcastle, November 23, 1646, AT IV 576; CSMK 304). Yet, he then adds that “though the animals do not perform any action which shows us that they think, still, since the organs of their bodies are not very different from ours, it may be conjectured that there is attached to these organs some thought such as we experience in ourselves, but of a very much less perfect kind” (Descartes to Newcastle, November 23, 1646, AT IV 576; CSMK 304 [emphasis added]). This entails that a strong mechanical reduction of bodily functions cannot avoid the fact that sensations, emotions, feelings, and passions are connected to a—at least— rudimentary kind of thought. As a result, a unified account of the cognitive structure of sensory experience concerns the animal nature—one should keep in mind that Descartes also speaks of a feeling of joy that he calls laetitia animalis in the Principia, somehow entailing that such a passion belongs to animals.21 The result is complex. As Gary Hatfield has recently summarized, Descartes’s attribution of feelings to animals cannot be reduced to a mere identity to human feelings, as animal feelings are “only corporeal counterparts to the passions: internal states that explain the animal behavior but that do not involve genuine feeling” (Hatfield 2008: 421). An ontological difference develops between animals and humans insofar as the rational soul is united to the human body alone, giving completion to the latter’s passions, feelings, emotions, and sensations. Yet, since these activities develop in the body, they should be explained within the mechanical framework of Descartes’s natural philosophy, and their mechanical parts pertain to animals as well as humans. Animals have feelings and experience passions, though in an unconscious form. As Gaukroger has claimed, in specifying the activities of animals “Descartes has to account for the behavior of sentient but non-conscious automata. Because automata lack a rational soul and so are literally ‘mindless’, this can only be done in terms of a mechanistic physiology” (Gaukroger 2002: 203). Nevertheless, Descartes’s interpretation appears fluctuant. On the one hand, the mechanical framework possibly explains all living functions—sensation included, as he reduced it to a hydraulic motion of particles. On the other hand, this does not entail an ontological identity between animals and machines, and apparently the explanation of these behaviors cannot be entirely mechanical but leaves room for some form of thinking within animal bodies. A discrepancy evidently emerges, especially in Descartes’s investigation of some particular cases in his late correspondence. Daniel Garber has brilliantly argued that, “even though all of an animal’s behavior can be explained mechanically, and even though there is no rational behavior that would force us to posit a soul, still we cannot absolutely exclude the possibility that God chose to create animals with souls, with thought and volition [. . .], the elimination of forms and qualities would only be probable. For with the bodies in general, as with animals, from the fact that behavior can be produced mechanically, it doesn’t follow that it is” (Garber 1992: 115–116). This entails that

21

Principia philosophiae, IV, art. 190, AT VIII-1 317.

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the reduction of animals to machines is mostly a philosophical tool to investigate animal physiology. Indeed, the mechanical reduction of animals to automata only specifies the physiological framework, helping to study bodily activities in a more scientific way, as is consistent with the principles of Descartes’s metaphysics and physics. Yet, this remains a hypothesis or a supposition, as he calls it in L’Homme, for animals are not machines in a strict sense, but nurture, grow, change, experience feelings and passions, store memories, and process information, even if in a very basic way—operations that machines do not perform completely. And when he investigates these features, his mechanization appears an insufficient explanatory tool. Descartes’s theoretical model of the animal-machine successfully expounds the physiology of bodily functions, but while this remains a physiological model to describe mechanical activities, the complexities of animal behavior exceed this reduction. From an ontological point of view, animals are neither machines (or inert bodies such as stones or salt) nor human beings, which are endowed with a rational soul. In order to understand animal nature and provide a natural philosophical section on animals, a study of a particular, existing being appears mandatory.

6.2

History of Animals: Movements, Instincts, Spirits, and Animal Life

More than in his published works, Descartes’s correspondence and Latin biomedical manuscripts reveal his discussion of animal behaviors—outlining a true laboratory of naturalistic studies. In the 1638 letter to Pollot, Descartes answers the objection that the experience reveals complex behavior, affections, and passions in diverse animals, and even a sort of language.22 Accordingly, one should differentiate the opinion acquired in childhood with the actual knowledge of animals. Grounded on the similarity between animal and human external actions, in childhood we were brought to believe that animals and humans display similar activities, but that similarity cannot be extended to the internal actions, according to Descartes. In contrast, one should conceive these states occurring in animals as differing from those in humans.23 Yet, Descartes failed to understand Pollot’s objection entirely and mostly fleshed out the physiological understanding of animal activities and their ontological differences with human nature. In concentrating on the singular parts of the body, he confirmed his mechanical reduction, while a study of particular bodies remained beyond his attention at this stage. A study of the singular parts or organs of bodies characterizes Descartes’s anatomical and physiological investigation. In a 1639 letter to Mersenne, Descartes claims that he has taken “into consideration [. . .] many particular things 22 23

Pollot to Reneri for Descartes, February 1638, AT I 514. Descartes to Reneri for Pollot, AT II 39–41; CSMK 99–100.

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Fig. 6.1 A dissected sheep drawn by Descartes. In René Descartes Excerpta anatomica, Appendix, AT XI, unpaged, Fig. XI

unmentioned by [scholars], which [he has] observed while dissecting various animals” (Descartes to Mersenne, February 20, 1639, AT II 525; CSMK 134). Through these ongoing observations, Descartes studied the number and arrangement of nerves, veins, bones, and other parts of an animal, adding observations to the mechanical supposition that grounds his physiology. Yet, Descartes’s program was not just to account for the principal parts of the body, separated from one another, as through anatomical dissections, but it importantly engaged with the body as a whole system. A few years earlier, in a 1632 letter to Mersenne, Descartes had, however, outlined this attention to the entirety of animal bodies, as he had performed observations, whose focus ranged from nutrition, the heartbeat, and the highest faculties, achieved through the “dissect[ions of] the heads of various animals [in order] to explain what imagination, memory, etc. consist in” (Descartes to Mersenne, October or November 1632, AT I 263; CSMK 40). Evidence of this investigation is collected in several fragments of Excerpta anatomica, in which the study of the animal body as a whole surfaces.24 This is especially highlighted by the representation of a dissected sheep (see Fig. 6.1). Another case surfaces in a fragment of a letter probably dated August 1630 and written to Mersenne, in which Descartes discusses an experience with frogs. Accordingly: [their] movement occurs thanks to the spirits, whose presence in a cavity of the brain could make it [i.e., the movement] persist even after the heart has been cut off; and new spirits flow in it from the blood contained in arteries. If, however, one cuts the head off, no spirit could flow towards the muscles [. . .] even though the heart continues to beat. As a consequence, no

24

Excerpta anatomica, AT XI 579–581.

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movement will endure, except those due to the spirits already present in the muscles, as one could observe in the tail of a lizard when cut off. [. . .] life does not consist in the movement of muscles, but in the heat within the heart. (Descartes to Mersenne, August 1630, AT IV 686; CM II 603 [translation is mine])25

In this letter, Descartes presents the living body as a system. In referring to the cases of frogs and lizards, which continue moving when vital organs are cut off because spirits are present within such moving parts of the body, he differentiates between these movements and life, and stresses that the living body is more than a mere sum of movements, for these may occur even when the parts are separated from the body. The movement of parts cut off from the main body does not entail that these parts are still alive, according to Descartes, who ultimately differentiates between the mechanics of motions and life. In this sense, a mechanical reduction could account for these movements, as the presence of spirits makes muscles inflate and move but fails to define the life of the whole body. The operation of the body as a whole system is thus more than the mere mechanization of the singular parts. The mechanical study of the singular part of the body is one thing; it is quite another to delineate the unity of many organic parts that would not operate when separated. A difference clearly arises between the reduction to mechanics and the interpretation of the body as a living system. On the one hand, Descartes reduced the activities of some parts to the mechanical reduction of his physics. This occurs in the correspondence with Regius, as by showing the movement of eels, Descartes challenges the ignorance of traditional scholars who attributed motions to a spiritual, immaterial principle. He claims that “the cause making those cut off parts of an eel moving does not differ from those that make the tip of heart beat, despite being cut off, or those that, in a cold and humid place, make chords contract [. . .]. While this later movement is called artificial and the first is called animal, in all these cases their cause is the arrangement of solid parts and the movement of spirits, namely of fluid parts permeating the solid one” (Descartes to Regius, November 1641, AT III 445 [translation is mine]).26 In disclosing the similarities between motions, be it the movement of an eel, a section of the heart cut off, or a movement of a chord, Descartes fleshed out that their cause is purely mechanical and does not rely on any animating principles scholars generally attributed to motion—and life. Something similar surfaces in his correspondence with Plemp, where Descartes attempted to buttress his explanation of the heartbeat and the circulation of the blood.27 In a series of observations on eels, he argues that “the fibers which make up the flesh of the heart are so disposed that the vapor of the blood which they contain is sufficient to make them swell up; the swelling up causes large pathways to open up [. . .]; thereafter the heart contracts, and so on. I was glad to see this

25 On Descartes’s principle of life, see Bitbol-Hespériès 1990. Bitbol-Hespériès 2000. Hutchins 2016. 26 See Bos 2002, 88. The paragraph reoccurs in Physiologia IV, see Bos 2002: 245–246. 27 Descartes to Plempius, March 23, 1643, AT II 66–68; CSMK 95–96.

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confirmed in another instance that I observed today. I cut off the upper part of the heart of an eel. . .” (Descartes to Plemp, 23 March 1643, AT II 68; CSMK 96). Descartes thus confirmed the mechanics of the heartbeat by means of observations. Yet, these observations concern some parts of the body, while no account for the whole system arises. On the other hand, Descartes discussed the cases of living bodies as a system or unity of functions disclosing life. In his correspondence with Mersenne, his interpretation of two histories or curiosities, according to which external bodies might grow on the human flesh, reveals this explanatory difference. The first story is the case of silk growing on the head of a girl, which according to Descartes depends on the fact that the skin growing on a scar takes the figure of the silk used to treat it. The second is the case of the thorn growing on the front of a Spaniard, which Descartes accounted for by claiming that: “the heat is a principle common to animals, plants, and other bodies, and one should not wonder that the same heat could make a man and a plant alive [together]” (Descartes to Mersenne, July 30, 1640, AT III 122 [translation is mine]). The difference relies on the fact that, while in the first case the singular part of the body took the shape and figure of silk, the second case shows that living natures are a system of interconnected parts, and no difference develops from a plant or human body. Another case concerns the movement of animals and its mechanization, and specifically as regards the flight of birds. In December 1639, Descartes described the force one needs to jump as similar to the mechanics of flights in birds.28 Later, as Mersenne informed him about an engineer who has devised a flying machine, Descartes points out that the flight of birds cannot be reproduced by such an invention, because “they flap their wings more or less depending on whether they need to stay still or move forward, a thing that cannot be imitated by any machine made by men” (Descartes to Mersenne, July 30, 1640, AT III 130 [translation is mine]). Although the mechanics of flight could be understood by men, devising a machine that reproduces it appears impossible to Descartes, as the necessity to fly (which is a sort of volition) cannot be reduced to mechanics, and the perfection of birds overcomes human skills.29 A month later, Descartes writes to Mersenne that “it is possible to make a flying machine like a bird, metaphysically speaking [metaphysice loquendo], because birds themselves are machines, according to [Descartes]; but it is not possible [to make them] physically or morally speaking, because they would need such subtle devices no man could fabricate” (Descartes to Mersenne, August 30, 1640, AT III 163–164 [italics in the text][translation is mine]). This letter contains a crucial aspect, as Descartes differentiated between (1) the physical equivalence of birds with flying machines, whose construction he considered impossible to achieve, and (2) the metaphysical claim that animals and birds are machines. Taken in itself, the flight of animals could be accounted for mechanically,

28

Descartes to Mersenne, December 25, 1639, AT II 629. One should note that in the Cogitationes privatae, Descartes reports the case of Archytas’s Pigeon, see AT X 232. 29

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and this is consistent with his metaphysics, while the realization of such machines uncovers a mechanical limitation. Accordingly, one could explain the movements of animals within the mechanical framework, and the movement of wings make birds stay still or move, but there is a perfection that cannot be reduced to mechanics, nor reproduced by human skills—as a difference between nature and automata develops. This reveals a discrepancy between the metaphysical framework, accounting for the singular motion in a geometrico-mechanical way, and the fact that actual birds are a system and not a mere mechanism. What makes the bird stay still or move cannot be mechanically reproduced or understood, as this depends on its volition, and thus escapes his mechanical physics. Similar to this case, Descartes discussed the swimming of fish. He paralleled the impetus in the movement of fish to the impulse a man follows to choose where to swim.30 As for the case of birds, a sort of volition specifies the mechanical movements of fishes. While Descartes generally embedded the movement of fish with the mechanical investigation of their body—two notes collected in Excerpta anatomica discuss the physiology of fish, while in La Description du corps humain Descartes discusses the formation of the heart in fish31—a more complex specification of animal nature emerges. On the one hand, Descartes explained these motions through the mechanical framework of his physics and following the principles of nature. On the other hand, either a volition or an impetus characterizes these motions, and this exceeds the mechanical reduction of nature, ultimately revealing animal bodies as complex systems. Related to this aspect, the question of instinct arises as an important issue for animal life. In L’Homme, Descartes specifies that what makes an animal-machine move is a combination of its innate structure or instincts, sensory stimulations, and the internal states of the organism.32 Yet, how his mechanical framework expounds instincts is unclear. In an October 1639 letter to Mersenne, Descartes discusses this point, claiming that: I distinguish two kinds of instinct. One is in us qua human beings, and is purely intellectual: it is the natural light or [mental intuition], on which, alone, one should rely on. The other belongs to us qua animals, and it is a certain impulse of nature towards the preservation of our body, towards the enjoyment of bodily pleasures, and so on. (Descartes to Mersenne, October 16, 1639, AT II 599; CSMK 140 [translation slightly modified])

Descartes differentiated between a mental intuition, which is a rational ability, and an animal impulse toward certain things. The former characterizes men, and the latter endows both animals and men. According to Vincent Aucante, one should read impetuosité, here translated with “impulse,” as impetus.33 This instinct is what makes animals move toward something, possibly with a goal-directed movement. 30

Descartes to Mersenne, February 1639, AT II 494. See Excerpta anatomica, AT XI 617–619. La Description du corps humain, AT XI 237. 32 Cf. Hatfield 2008: 418. See L’Homme, AT XI 192–195. 33 See Aucante 2000: 223–226. 31

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In a note collected in Primae Cogitationes, and probably dated 1637, Descartes specifies how instincts are formed in animals. Since animals move in various ways, their brains should have diverse arrangements, which originate from two elements, “being advantageous for their nature or disadvantageous for their nature. When sensation acknowledges something as advantageous, [. . .] the body moves to acquire such advantage” (Primae Cogitationes, AT XI 519 [translation is mine]) and vice versa. In many cases, instincts are innate and mechanically shaped and do not depend on cognition, but on the fact that “while being in the uterus of their mothers, [fetuses undergo a number of conditions, both] advantageous or disadvantageous, through which they grow and have been moved to determinate movements; and when something similar occurred again, they made the same movement” (Primae Cogitationes, AT XI 520 [translation is mine]). Similarly to the case of birthmarks, Descartes claims that instincts originate in the uterus, as the brain of the fetus acquires the notions that something is useful or dangerous from the brain of the mother. As Descartes writes in a note of Excerpta anatomica, “the fetus in the uterus is nurtured by the blood of the mother [. . .], that blood could be imbued with the forms or ideas lying in her fantasy, from which originate the birthmarks” (Excerpta anatomica, AT XI 606 [translation is mine]). When something occurs in the brain, a certain arrangement of particles shapes the nervous impulses that reach the fetus, affecting its body, in the case of birthmarks, or its brain, in the case of instincts. In other cases, “if the imagination of the mother is harmed [ex laesa], the fetus develops monstrous parts” (Primae Cogitationes, AT XI 518 [translation is mine]). According to Descartes, mechanical reasons uncover such correspondences (which he also calls sympathies) and accounts for the origins of instincts.34 Instincts are nothing but the arrangement of particles in the brain, whose origins lie in the movement of particles from the brain of the mother to the fetus. This origin is entirely mechanical. In these notes, Descartes fleshed out how much the instinctual knowledge of what is harmful for the body, or when to run from a danger, relies on the mechanical arrangement of the brain while being formed in the womb. Yet, Descartes used another example to prove this point. Training proves that, in recurring experiences, particles arrange in the brain teaching the animal whether an experience is useful or harmful. For this reason, “if you whipped a dog five or six times to the sound of a violin, it would begin to howl and run away as soon as it heard that music again” (Descartes to Mersenne, March 18, 1630, AT I 134; CSMK 20). In the brain of the dog, the harmful experience of being whipped is associated to the sound of violin; therefore, the dog develops the instinctual knowledge—a material memory consistent to the physiology of L’Homme—that when one plays the violin, something dangerous occurs to him, and he is going to run away. In all these cases, Descartes clung to the mechanical framework of his physics. As he was confronted with a diversity of animal phenomena, from instincts to movements, from the circulation of spirits to animal life, Descartes spelled out all these

34

Cf. Descartes to Mersenne, July 30, 1640, AT III 120–121; CSMK 148.

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cases consistently with his mechanical physics. The anatomical observations of animal bodies, from the experiments with a chicken, chicks, pregnant cows, and so on, a list of which is in Descartes’s 1646 letter to Mersenne,35 did help him observe his mechanical physics in nature. Still a limitation surfaces, as Descartes claimed that there are some volitions or impulses that do not follow this mechanical framework entirely. The latter works in the account of the formation of such instincts but cannot operate in explaining them. Instincts and volitions present therefore the limit of Descartes’s physical mechanization of animals, somehow revealing that living bodies are more than a mere aggregate of particles. Mechanization operates in explaining the origins of such behaviors but cannot produce a more exhaustive explanation of animal activities. Moreover, differences between particular animals surface in Descartes’s work, as I am going to explore in the next section.

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A Mechanical Scale of Animals: Brutes, Dogs, Cows, Fish, Birds, and Oysters

In the first note collected in Primae Cogitationes circa generationem animalium, probably from the early 1630s, Descartes differentiates between generation “without seed or the uterus, and generation from the seed” (Primae Cogitationes, AT XI 505; Aucante 2000: 29 [translation is mine]). Before delving into this difference, Descartes acknowledges that there are common activities to “animate bodies, such as spontaneous movement, nutrition, etc., and one should examine these first. Then, there are other activities common to most of them, like sight, hearing, etc. [. . .] and one should understand why these are not in all. Some issues are subordinate to the main genre, being biped for all birds, quadruped for beasts, having fins for fish, having more feet for insects, etc. Fourth, one should explore the singular and low grade species” (Primae Cogitationes, AT XI 505 [translation is mine]). This short list unearths an early attempt to classify animate bodies, specifically animals, by means of their activities: This list goes from the most common operations, such as self-motion and nutrition, to the less common such as sensation, and so on. This entails that the more we proceed toward complex activities, i.e., sensation, imagination, emotions, and cognition, the more uncommon such operations are in animals. While all animals share the most basic activities, from the low grade species to the highest and more complex bodies, the so-called higher faculties are shared by fewer species that are closer to human beings. In this section, I try to reconstruct a scale of animal bodies following this line, moving from the most common activities, namely the vegetative processes of generation and nutrition, to the most complex. Indeed, in claiming that other characteristics are common to particular species, Descartes differentiates between volatiles, mammals, fish, and insects, as they have exterior differences as a consequence of their nature. 35

Descartes to Mersenne, November 2, 1646, AT IV 555.

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One of the first notes of this manuscript provides an investigation into generation without a uterus. This uncovers a differentiation between less and more complex animal bodies. For instance, while generation is a common process in living beings, breeding within or without a uterus entails a mechanical diversity and an organic complexity according to Descartes. As previously highlighted in Sect. 5.1, a difference along this line arises between vegetal and animal bodies. A mechanical gradation shows the differences between the generation of plants, from seeds sown in the earth or in some other elements, and the generation of animals, whose seeds need to be implanted in a uterus.36 The same could be said for this paragraph on the difference of generation outside or inside the uterus. This is the text: The principle is that a source of heat could excite two subjects, making one of them expel the subtle parts (which [he] will later call vital spirits), and from the other the coarser parts (to be named blood or vital humor); and these parts will cooperate together generating life in the heart [. . .] and later the brain. For this reason, since few things are necessary to generate an animal, it is not astonishing if many animals, worms, insects generate spontaneously from putrid matter. At this stage, one should note that the two subjects requested are the lung and the liver. . . (Primae Cogitationes, AT XI 505-506 [translation is mine])37

This note contains some aspects of Descartes’s embryology. First, the main principle is that heat excites particles. Second, in order to kindle life, heat should work on two very specific subjects or amounts of matter, one is aerial, or what he later calls vital spirits, and the other is liquid, as Descartes defined it as blood or vital humor. The combination of a vital spirit and a vital humor, plus the presence of heat, generates life. Since this apparently is little matter, Descartes appeared inclined to spontaneous generation from putrid matter.38 Yet, he then specified the nature of these two elements, which he claimed to be (at least similar to) the lung and the liver. Thus, a reduction of vital elements to material organs surfaces, but this is not a complete reduction of life to extended matter, as this material is not undistinguished. In this process, the first organ expels vital spirits and the second organ expels vital humor. The combination of such elements produces a movement in the heart. Only at this point, that is when the heart is formed and beating, does the animal exist, according to Descartes. Despite being produced outside the uterus, Descartes recognized some common traits in generation, as one can infer from his other work on generation. The presence of vital organs, namely the lung and the liver, the combination of matter, the formation of the brain, and the formation and movement of the heart provide a mechanical framework to understand generation in animals. Yet, this note reveals something more. Indeed, in discussing generation without the uterus, Descartes speaks of low-grade species. 36

See Primae Cogitationes, AT XI 534–535. La Description du corps humain, IV, AT XI 253. A similar account is in a December 1637 note of the Excerpta anatomica, AT XI 599–600. Aucante argued that the order of generation of organs unearths a transformation in Descartes’s understanding of generation throughout the time, but I disagree on this point, as these two notes from different periods show. 38 On this issue, see Farley 1977: 8–13. Garber 2022. 37

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In a further note, Descartes described zoophytes, or bodies that stand between the vegetal and animal realm. In doing so, he attempted to locate these organs. Such bodies are “oysters, sponges, etc., [which have] a stone in the place of the liver and water or air in the place of the lung to ignite life. As a consequence, these bodies have nothing but flesh and heart, and perhaps the brain; which in oysters is made by a nerve through which they close themselves. And for this reason, such bodies do not change place, for they would die after leaving their lung and liver” (Primae Cogitationes, AT XI 520 [translation is mine]). Although Descartes considered these animals as “too imperfect” (Descartes to Cavendish, November 23, 1646, AT IV 576; CSMK 304), he, however, provided them with life, as some parts (external to the body) take the place of vital organs and produce life. Yet, their imperfection makes generation occur outside these bodies, as he writes in a November 1637 note in Excerpta anatomica, where he compares “plants without seed [. . .] and the most imperfect animals, such as oysters, which do not generate their analogous [body]” (Excerpta anatomica, AT XI 527 [translation is mine]). In these low grade species, living bodies result from the combination of matter activated by a source of heat. From these cases, Descartes provided a mechanical explanation of life and generation. While oysters, zoophytes, and insects are the lowest grade of animals, Descartes drew attention to the study of more complex animals, those that generate their offspring in the uterus. Regrettably, Descartes failed to define a scale between such bodies, as he was probably uninterested in such a division. Yet, following the previous list, I will first concentrate on Descartes’s description of fish and birds, and especially his study of chicks, as they share very few functions with the human bodies, then I will focus on calves and dogs, whose structure and behavior are more similar to humans, and finally on brutes. As already noted, fish are the subjects of investigation in the correspondence with Plemp concerning the heartbeat. While Plemp considered fish to be cold animals, Descartes argues that “even if we do not feel much heat in fishes, their hearts do feel hotter than any other organs in their body” (Descartes to Plempius, February 15, 1638, AT I 529; CSMK 83).39 In two notes of Excerpta anatomica, Descartes describes his observation of a codfish (or cabeliau) and a stock fish. In the first case, he describes the intestines, which are “curled up in three folds [plicas], as in this figure [see Fig. 6.2] [. . .] and many fibers compose the stomach [and are detected] from the teeth, as in the palate of oxen” (Excerpta anatomica, AT XI 617 [translation Fig. 6.2 The representation of the cod intestines. In René Descartes, Exerpta anatomica, Appendix, AT XI, unpaged, Fig. XVIII

39

Cf. Descartes to Plempius, March 23, 1638, AT II 66–67.

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is mine]). Then, Descartes observed the order of organs, which are tinier and closer if compared to other animals. In this fish, the “gall-bladder is bluish, the spleen very reddish and lavish, while the liver is white; and this confirms my opinion that the blood that comes from the spleen to the liver mixes with the chyle, which becomes red in the heart. Furthermore, these fish do not need a big liver” (Excerpta anatomica, AT XI AT XI 617–618 [translation is mine]). Similarly for the second fish, probably another kind of codfish, Descartes noted the tiny dimension of the organs, the whitish color of the liver, the red color of the spleen, and the reddish color of the gallbladder. As he writes: In the place of nostrils, it has two deep and extended holes [see Fig. 6.3] [. . .] moreover, there is a bladder that separates the esophagus from the backbone [. . .]. Undoubtedly, in this kind of fish, the circulation of blood proceeds from the heart through the gill to the head, and from there to the lower part of the backbone towards the tail, then to the spleen, from the spleen to the liver and the intestines [. . .]. The organ of hearing could be located in the gills, as they are bony parts. Nerves reaching the brain through the posterior part of the backbone, not its median part.” (Excerpta anatomica, AT XI 618–619 [translation is mine])

In these notes, Descartes mostly focused on the anatomical arrangement of organs and their size and color, which he connected to their functions. For example, the liver is white, as it especially collects the chyle, which is later mixed with blood. Furthermore, Descartes drew a few pictures of such organs, dealing with their size and arrangement (see Fig. 6.2 and 6.3). Another important aspect is the detection of a bladder. In a 1639 letter to Mersenne, Descartes stresses that “fish do not need a bladder to swim, since many of them do not possess it” (Descartes to Mersenne, February 9, 1639, AT II 494 [translation is mine]) whether or not he was referring to the bladder examined in the stock fish is not clear. In the last part of the note, he also focused on sensation and in the arrangement of nerves in fish. Undoubtedly, fish have a simple body, which in the mechanical terms of Descartes’s natural philosophy entails that processes are more easily observable. Indeed, Descartes observed fish to derive some knowledge concerning the heart as the seat of an internal heat, thus confirming his theory, or to understand other living functions. Additionally, a mechanical definition of fish ultimately surfaces. Close to fish, birds too display a simple body. Besides the reflections already noted, Descartes mostly concentrates on the study of the eggs of chickens. In following the work of Hyeronimus Fabricius ab Aquapendente (1537–1619) (and

Fig. 6.3 The representation of a hole that replaces nostrils in the cod. In René Descartes, Excerpta anatomica, Appendix, AT XI, unpaged, Fig. XXI

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Aristotle before him), Descartes performed several observations on eggs as a way to unearth the earlier moments in the formation of fetuses. Several pages of Excerpta anatomica collect such observations.40 Descartes attentively observed the arrangement of the organs in chicks and inferred that “the animal spirits are collected in the albumen, as all limbs form in it, as it occurs in the seeds of quadrupeds” (Excerpta anatomica, AT XI 616 [translation is mine]). Accordingly, the yolk and the albumen play a role similar to the membranes that wrap the fetuses of quadrupeds, i.e., mammals. Then, Descartes observes that “the heart is not formed in the middle of the seed, but in one of its extremities, in the way we see that, in the seeds of plants, the germinating parts are at one extremity” (Excerpta anatomica, AT XI 616 [translation is mine]).41 Moving from an observation on chicks and eggs, Descartes investigates the position of the heart within the fetus. Not only does this have a structural significance, but it also reveals a temporal meaning concerning the order of the formation of the fetus, ultimately confirming that the heart is not the first organ to be formed. This is strongly consistent with Cartesian embryology. As he later writes in a February 1648 note, if the heart was the first organ, “all its parts [of the fetus] would be twisted,” because “the heart bends the blood more in the left side” (Excerpta anatomica, AT XI 608 [translation is mine]) of the body. Yet, the observations on eggs (and plant seeds) confirm that the heart is not at the center of the fetus, therefore entailing that this is not the first organ to be formed. In another note, Descartes reports the dissection of more than 30 chicks at different days of generation, from day 2 to day 19 of fecundation. In all these cases, he jots down the diverse phases in the formation of organs.42 In observing the fetuses of chicks, Descartes thus establishes an order in the formation of organs, ultimately using experimentation to confirm his theory of animal generation. Being generated from eggs, birds are thus a suitable case study for Descartes’s mechanization of embryology, as he could note the order of formation of organs and limbs with more precision. Yet, a larger number of notes on generation focuses on calves and cows. These have a double aim. The one is embryological, and such notes could probably be combined with the study collected in Primae Cogitationes. The second is functional, as Descartes investigates the processes of life, and especially the heartbeat by dealing with the anatomical observations of organs. Excerpta anatomica starts with a note on the heart of a calf.43 And then several more notes on younger calves.44 In these observations, Descartes focuses on the heart and its valves, the arrangement of veins and vessels, and such observations comply with his physiological theory. It is possible that he had performed such observations in the early 1630s. Then, he explores the nature of the liver,

40

See Excerpta anatomica, AT XI 614–617, 619–621. Cf. Baldassarri 2021a: 195. This parallel with plants is not unimportant. See Chap. 5 on the issue of living bodies generation. Cf. Baldassarri 2021a: 186–191, 197–199, and Figs. 5.1, 5.3, and 5.4 in these pages. 42 Cf. Excerpta anatomica, AT XI 620–621. 43 Cf. Excerpta anatomica, AT XI 549–552. 44 Cf. Excerpta anatomica, AT XI 553–554, 554–556, 556–564. 41

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gallbladder, lungs, spleen, and nerves, as his anatomical dissection continued in focusing on the valves and fibers composing the parts of the body.45 These notes compose a large number of anatomical investigations, in which Descartes pays attention to the structure of organs and the different parts of calves, and have the shape of laboratorial notes on the animal body, rather than of a medical textbook. Again in the following sections, Descartes explores the structure of calf fetuses or calves born early.46 He aims at inspecting the arrangement of organs and the constitution of the diverse parts. It is probable that he used these embryological observations to buttress his reasoning concerning the order in the formation of the fetus he later developed in La Description du corps humain.47 In the following note, Descartes deals with the structure of a sheep brain and its nerves, focusing on their disposition and shape.48 Then, he investigates the structures of the ears and the auditory nerve, and then the optic nerve.49 This part contains the observation on the nervous system Descartes claimed to be performing in the 1632 letter to Mersenne. Still, these notes fail to elucidate the mechanical functioning of organs but mostly focus on the mechanical arrangement of these parts. In the section entitled “Observationum Anatomicarum Compendium de partibus inferiori ventre contentis” [Compendium of the anatomical observations of the inferior parts contained in the abdomen], Descartes collects several observations focusing on the arrangement and structural shape of the organs in the abdomen.50 This section also sheds light on the nature of such organs and, though partially, on their functioning. For example, Descartes discusses the pancreas, the interrelation between stomach, spleen, gallbladder, and liver, as well as the anatomical structure of the stomach. The pictures collected in the Appendix of Excerpta anatomica reveal Descartes’s attention to several of such details, ranging from the disposition of vessels and the heart to the arrangement of organs.51 Insofar as they display a more complex body, calves and sheep are suitable case studies to observe the arrangement of organs and their interconnections, as well as their formation. While in fish and chicks Descartes could observe the disposition of organs, in mammals, he could inspect smaller details or other parts beyond the mere structure of organs and shed light on the structure of vessels, focusing on large-scale bodies. For instance, the observations of the parts composing the ear and the auditory nerve, brain, and other nerves could be easily performed on larger animals that display a similar structure to humans.

45

Cf. Excerpta anatomica, AT XI 564–573. Cf. Excerpta anatomica, AT XI 574–577, 577–578, 583–587. 47 I am not entering this discussion, but connections have been detected. See the notes in the Italian edition of La Description du corps humain, in Belgioioso, Opere postume: 509–597. 48 Cf. Excerpta anatomica, AT XI 579–581. 49 Cf. Excerpta anatomica, AT XI 581–583. 50 Cf. Excerpta anatomica, AT XI 587–594. For a translation of the Compendium, see Baldassarri 2023c. 51 Cf. Excerpta anatomica, Appendix. See Belgioioso, Opere postume: 1214–1215. 46

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Although there is no frame of a scale of beings, in these notes, Descartes seems to entail that, while smaller animals are easier to observe, larger animals help grasp the mechanical structure and arrangement of parts and organs in a clearer way. Indeed, Descartes draws a difference between the animal-machines. For instance, in the letter to Plemp published by Beverwijck in 1644, Descartes suggests a structural difference between the heart of a rabbit, “a docile animal [timido animali]” (Descartes to Plempius, February 15, 1638, AT I 528n [translation is mine]) and the heart of dogs. Accordingly, “in dogs, heart ventricles have diverse ravines, whose singular cavities are extended by the dilation of blood in a way that the entire cavity of the ventricle appears smaller. This perhaps misled those who judged the heart tightening during systole” (Descartes to Plempius, February 15, 1638, AT I 528n [translation is mine]). These few lines contain a captivating passage, which unfortunately remains with no further explanation. Descartes proclaims that the heart of more docile animals effectively suits the exploration of its functioning, while the more complex heart of dogs could mislead the anatomist, because it contains several singular cavities. Apparently, he connects the indocility of animals like dogs with the capacity of their heart to inflate more promptly, therefore suggesting that the behavior of animals depends on their diverse bodily structures, but this point remains regrettably unclear. What is interesting for us is that a mechanical difference arises between animals, as some of them suit better the goals of anatomists. At the same time, dogs appear to be suitable bodies for exploring the intestines. In 1640, Descartes wrote to Huygens that he had “observed the bowels of living dogs, which have a regular movement, as the one of respiration” (Descartes to Mersenne, July 30, 1640, AT III 141 [translation is mine]).52 Dog vivisection was part of Descartes’s study of the lacteal vessels, a glamorous subject of investigation in the Dutch Provinces at the time (Fig. 6.4).53 As it surfaces, Descartes studied the anatomy of animal bodies to focus on their structure, to shed light on their generation, nutrition, and blood circulation, and therefore to understand living functions in general. Yet, he did not restrict such an interest to the basic operations of life, but also concentrated on sensation and instincts, as he observed the nervous system and the arrangement of organs. In the Discours, Descartes claims that the anatomical study of the nervous system shows what makes animal bodies move, “as when [. . .] severed heads continue to move about and bite the earth although they are no longer alive,” and continues claiming that he also has: indicated what changes must occur in the brain in order to cause waking, sleep and dreams; how light, sounds, smells, tastes, heat and the other qualities of external objects can imprint various ideas on the brain through the mediation of the senses; and how hunger, thirst, and the other internal passions can also send their ideas there. And [he] explained which part of the brain must be taken to be the ‘common’ sense, where these ideas are received; the memory, which preserves them; and the corporeal imagination, which can change them in

52 53

Cf. Descartes to Regius, May 1641, AT III 374. See Trevisani 1992: 244. Meschini 2015. Baldassarri 2021a: 57–58, 169–173.

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Fig. 6.4 The illustration of a dog dissection to inspect the organs of the abdomen. In Henricus Regius, Fundamenta physices, cap. X, 171

various way [. . .] in a manner which is just as appropriate to the objects of the senses and the internal passions. (Discours de la Méthode V, AT VI 55; CSM I 139)

Although Descartes clearly refers to the human body alone—namely a machine without the mind—one could probably derive that these activities pertain to the body alone, and in this sense they are common to the animal and human bodies, as I have already discussed. Among these common activities, Descartes includes sensation, imagination, and memory, as well as internal feelings and passions, insofar as these operations occur in the body, and somehow depend on the anatomical structure, while having nothing to do with the mind or soul. Additionally, in the letter to Cavendish examined earlier, Descartes extends the animal behavior to a form of thinking, as he writes that “though the animals do not perform any action which shows us that they think, still, since the organs of their bodies are not very different from ours, it may be conjectured that there is attached to these organs some thought such as we experience in ourselves but of a very much less perfect kind” (Descartes to Newcastle, November 23, 1646, AT IV 576; CSMK 304). In this sense, the closer he came to human bodies, in a mechanical scale of beings that follows their mechanical complexity, the more these bodies display sensation, emotions, memory, and imagination, which are similar to human nature. Finally, Descartes attributes a

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rudimentary thought to animals, in connection with their instinct,54 but these faculties are only corporeal—of course, this aspect intersects with the immortality of the soul, an issue I am not going to investigate here. The next group of bodies concerns what Descartes calls brutes.55 Probably, Descartes considers brutes as a general group of animals displaying mechanical and corporeal higher functions. One should note that, in Fundamenta physices, Regius devotes an entire, though short chapter, to brutes [De Bestia], placed between the chapter on animals and the chapter on humans. According to Regius, brutes are “mere animal[s], whose sensible and moving actions occur due to the sole disposition of the particles as in automata, and without any cognition, intellect or intelligence” (Regius, Fundamenta physices: cap. XI, 241 [translation is mine]). In Regius, brutes are gathered in the animal kingdom, while the only difference with humans is the fact these latter possess a mind. Descartes’s understanding of brutes is consistent with such a distinction, as he claims that brutes are animals in general which behave following the disposition of the body and lack a mind. Yet, his discussion presents some interesting issues. In the Regulae, Descartes affirms that “memory is no different from imagination – at least the memory which is corporeal and similar to the one which brutes [brutorum] possess” (Regulae ad directionem ingenii XII, AT X 416; CSM I 43 [translation slightly modified]). In the Fourth Responses, referring to the Discours and to L’Homme, he repeats the claim that “both in our [i.e, human] bodies and those of the brutes, no movements can occur without the presence of all the organs or instruments which would enable the same movements to be produced in a machine. [. . .] a very large number of motions occurring inside us do not depend in any way on the mind. [. . .] All the actions of the brutes resemble only those which occur in us without any assistance from the mind” (Fourth Responses, AT VII 229–230; CSM II 161). Probably, he considers brutes as very similar to humans, for their bodies appear very similar and they display a similar behavior. In a large note of Primae Cogitationes, Descartes describes brutes in relation to the animal instincts and to the mechanical tendency to pursue the advantages [commoda] or flee the disadvantages [incommoda] of nature.56 Accordingly, such movements do not depend on volition, but on the dispositions of the brain, which are diverse and abundant in brutes as well as mechanically established. As for the case of instinct, the arrangement of particles in the brain allows the brutes to acknowledge something as advantageous or disadvantageous. When something touches their

54

See Simmons 2003: 550. See Curth 2010. 56 For a discussion of commoda and incommoda, see Meditationes de prima philosophia, VI, AT VII 74–75. See Chap. 5. A similar instinctual behavior surfaces in Florent Schuyl’s description of the movement of tulips, written in the Preface of his Latin translation of L’Homme, where he includes an important mechanization of plants consistent with Cartesian philosophy. Schuyl, De homine: Ad lectorem, unpaged: tulips “void of all cognition, automatically opens its flower to receive the morning sunlight, and closes it again in the evening to preserve its seed from the harmful cold of the night.” Cf. Baldassarri 2021c: 271; Raymond 2023. 55

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senses, the nervous impulse reaches the brain and lets the body recognize or recollect whether it is advantageous or not, and to draw benefit from it or not.57 This concerns their corporeal memory. Insofar as the latter depends on the shape and figures nervous impulses draw in the brain, brutes have recollection of things, as they experience whether such events are harmful or beneficial to the body and behave accordingly. A mechanical interconnection between the nervous system, corporeal memory, and instinct characterizes Descartes’s study of brutes. Yet, since no intellectual memory surfaces,58 the behaviors of brutes necessarily depend on their mechanical construction, and they have no freedom and do not sin, and their operations are flawless. As a consequence, Descartes affirms that the experience of brutes is corporeal and significantly differs from human cognition. A few lines later, he adds that “brutes lack any cognition of what is advantageous or disadvantageous; [for they have acquired such experience] while being in the uterus and advantages or disadvantages help them grow and perform a movement [which] they repeat when the same advantageous thing occurred again” (Primae Cogitationes, AT XI 520 [translation is mine and slightly adapted]). Brutes’s behavior thus relies entirely on the corporeal arrangement of matter that follows the mechanical reduction of living bodies, and they have neither conscience nor cognition. This helps specify what he had written to Cavendish, concerning a rudimentary form of thinking in animals, as Descartes seems to reduce animal instinct to a mechanical order. This description is consistent with article 52 of the Passions of the Soul, where Descartes stresses the interaction with the environment produces bodily stimuli—he affirms that, “the objects which stimulate the senses do not excite different passions in us because of difference in the objects, but only because of the various ways in which they may harm or benefit us” (Les Passions de l’âme, II, art. 52, AT XI 372; CSM I 349). Yet, while in humans such stimuli dispose of the soul to a specific volition, in the case of brutes, stimuli make the body move, without any intervention of the mind. Later in the Passions, Descartes refers to brutes as violent men who generally misbehave or follow their passions without the mediation of the mind.59 Not unexpectedly, in the 1664 Preface to the French edition of L’Homme, Claude Clerselier claims that “a great similarity [surfaces] between humans and brutes [les bêtes] both in the conformation of their bodies and in the conformation of their actions” (Clerselier, Preface: 50).60 In this sense, brutes appear to be like animals with a complete set of living activities, even the highest corporeal one, and not dissimilar to humans who little (or rudimentarily) use their minds.

57

Primae Cogitationes, AT XI 519. Primae Cogitationes, AT XI 519–520. 59 See Les Passions de l’âme, II, art. 82, AT XI 389; III, art. 188, AT XI 470; art. 194, AT XI 474. 60 In Belgioioso Opere postume: 660 [translation is mine]. 58

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The Mechanical Life of Animals

Undoubtedly, Descartes’s observations of animal bodies shape his understanding of animal nature in a way that is consistent with the principles of his mechanical physics. In investigating the embryological origins of living functions, Descartes provides a mechanical account of animal instincts, sensation, memory, and emotions, by means of the movement and arrangement of particles, and the mechanical functioning of organs. Yet, both providing animals with perception and sensation, and discussing the differences between particular animals reveal salient problems in his definition of animals as machines. Indeed, despite reducing animal behaviors to a mechanical order, he opens to some activities that do not pertain to machines, which results in restricting the heuristic role of the mechanical reduction, while a complete identification of animals and machines appears more and more improbable. Animals are not just a mechanical configuration of matter but also have an internal unity. As Dennis Des Chene has discussed, Descartes “treats animals and plants and their organs as phenomenal unities” (Des Chene 2001: 116), as they have a physical unity (i.e., a common motion), a dispositional unity (namely the arrangement of their organs), and a functional unity (as these organs have a purpose). Animals reveal an organic system, made of organs mechanically arranged and operating, but cohesively working. In this sense, an animal is more than the mechanical addition of single organs, and Descartes’s mechanization is a model to grasp the arrangement and functioning of parts, but there is something more, as the living body is a systematic unity—whose complexities emerged in the previous sections on particular animals. An asymmetry surfaces between the anatomical study of organs and singular functions, which “proceed from matter and [. . .] depend solely on the disposition of our organs” (L’Homme, AT XI 120; G 99), and the fact that life results from the unity of all the parts. According to Descartes’s mechanical framework, the organ creates the function in physiology, but what allows functions to exist is the unity of all the organs. The circulation of blood is meaningless if one observes a heart separated from the vessels and the other parts of the body. In this way, although Descartes grounded his study of living bodies on anatomical observations, he did not spend time describing any anatomical investigation in his text, but focused directly on explaining the “movements [. . .] in the proper order and [. . .] to tell [. . .] which of our functions these [movements] represent” (L’Homme, AT XI 121; G 100).61 Additionally, at the beginning of L’Homme, Descartes represents the living body as a unity of functions (see Fig. 6.5). Taken from a mere physical unity, that is, as a unity of movements, the animal body is thus nothing but a hydraulic machine in which blood circulates and fluids move from one part to another. This occurs not only in the circulation of the blood but also in nutrition, growth, reproduction, as well as sensation; Descartes

61

On the division between anatomy and physiology in the early modern time, see Andrault 2016.

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Fig. 6.5 The unity of organs in the living body. In René Descartes, L’Homme, AT XI 128

appropriately reduces all such functions to a hydraulic motion of fluids and particles.62 Yet, already in such a case, the unity of organs appears to be directed toward a purpose, if not even toward the production of a designated operation.63 A more complete interpretation of Descartes’s physiology concerning teleology and ends has been a matter of discussion recently, but I am not entering this debate. Yet, what I want to highlight in this section is that Descartes’s physiological aim is to describe the functioning of the entire body as a whole, namely as a unity. Beyond the reduction to automata, for Descartes, an animal is an organic entirety and a unity of functions and living activities, and one may account for living beings as a system. I move from three cases, and then focus on Descartes’s interpretation of life that follows from this understanding of living bodies as a unity of processes. Three main cases are particularly striking: digestion, connection between brain and intestines, and birthmarks. All of these cases reveal an interconnection between different organs and parts of the living body that unearths a unity of processes proceeding beyond the mechanical addition of operations, or the mechanical aggregation of organs. In a well-studied 1630 letter to Mersenne, Descartes asked whether animal bodies should be sorted into three parts: the head, the chest, and the abdomen

62

See L’Homme, AT XI 125–130. See Des Chene 2001: 122–140. Cf. Simmons 2001; Manning 2013; Distelzweig 2015; Meschini 2015 and 2018. 63

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[caput, pectus, et ventrem],64 a traditional way of differentiating between the parts of the body in anatomical treatises. Yet, while Descartes refrained from following the traditional ways of writing about living bodies, it seems that he also pursued a diverse investigation of living processes. This would ultimately help me shed light on Descartes’s understanding of (animal) life within his mechanical framework. In a short section collected in the Compendium on the Abdomen, dated 1637, Descartes shed some important light on the structure of the organs in the abdomen. Although he had discussed digestion and nutrition in L’Homme, these activities remained under-specified in his early physiology. While showing the role of the circulation of blood for nutrition and the role of blood issuing from the heart in activating digestion, Descartes refrained from specifying the role of each organ in the abdomen.65 The Compendium provides a different perspective. Besides the anatomical description of organs and the disposition of diverse parts, Descartes adds something relevant. In listing the organs connected to the portal vein, such as the intestines, the stomach, the mesentery, the omentum, the pancreas, the spleen, and the gallbladder, as well as the liver, Descartes also specifies a connection between the stomach and the spleen: “some acid blood goes from the spleen to the stomach, [. . .] and some juice [goes] from the stomach to the spleen, where it sours [acescit]” (Excerpta anatomica, AT XI 590 [translation is mine]). This point should not be underestimated, as he describes a crucial activity related to digestion. The movement of acid juices from the spleen to the stomach eases digestion, according to him. Although the blood still plays a central role, one should note that, in this case the blood does not issue directly from the heart, but the organs in the abdomen perform some work on it. Several paragraphs later, Descartes describes the structure of the stomach. This is composed of straight fibers, while the intestines have transversal fibers. Moreover, it possesses many nerves, which Descartes connected to the formation of the stomach from particles issuing from the brain.66 Accordingly, the stomach acquires a more autonomous physiological structure. While in L’Homme Descartes conceives of the stomach as a mere receptacle of food—the notorious metaphor of the barn in which new hay is stored—and digestion occurs by the force of the blood issuing from the heart,67 in this later note the stomach has a more precise structure, a precise connection with the organs of the abdomen, and an autonomous functioning. Moreover, Descartes unearths an embryological connection between the brain and the abdomen. On the one hand, he stresses the autonomy of the abdomen, where the production of juices to ease digestion occurs; on the other hand, he extends the

64

Descartes to Mersenne, 23 December 1630, AT I 196. A reconstruction of this is in Baldassarri 2018c. 66 Excerpta anatomica, AT XI 594: “In ventriculo, observo intus illum habere fibras rectas [. . .]. Item, illum habere multos nervos [. . .]. Ex quibus conjicio, totum ductum ab ore ad podicem ortum habere ab excrementis e cerebro delabentibus. . .” For a translation, see Baldassarri 2023c. 67 L’Homme, AT XI 121. 65

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connection between organs not only to the heart but also to the brain. As a result, the entire body discloses an interconnection of functions. This especially emerges in his embryological work, where Descartes fleshes out a connection between, if not even a sequence in, the formation of the brain and the formation of intestines and stomach, which follow from the former. Accordingly, whenever the brain grows, particles move from it and compose the various limbs. This especially concerns the organs of sensation, and also the organs containing nerve endings. For instance, these particles compose the esophagus, the stomach, and the intestines. As he wrote, “the excrescences [excrementa] of the brain are different [. . .]. First, [. . .] it grows an exhalation [flatus quidam valde humidus] [. . .] descending through the esophagus, [it] inflates the stomach, and several nerves [. . .] flow. Moreover, one should note that the entire substance composing the esophagus and the stomach flows from the palate or, better, from the excrescences of the brain” (Primae Cogitationes circa generationem animalium, AT XI 512 [translation is mine]). According to Descartes, a humor goes from the brain to the abdomen, shaping the different organs and parts of it. He then describes this order of formation in more detail, concluding that: “all these things come from the excrescences of the middle cerebral ventricle” (Primae Cogitationes circa generationem animalium, AT XI 513 [translation is mine]). In another note of Primae Cogitationes, probably dated 1637,68 Descartes specifies the brain–abdomen connection in more detail. Following a Galenic tenet, he distinguishes between the noble organs, such as the brain, heart, and liver, which are formed first, and the ignoble organs, such as the spleen. Moreover, he differentiates between spleen and gallbladder, which are formed by the artery, and stomach and intestines, “formed in a later moment through the excrescences of the brain; they have a great number of nerves” (Primae Cogitationes circa generationem animalium, AT XI 517 [translation is mine]). The fact that several nerves are situated in the stomach and the intestines is the evidence of such an embryological connection. Descartes repeated this issue in a December 1637 note of Excerpta anatomica, where he claims that “the principal excrescence of the brain is a humor similar to the pus within its ventricles, made from the spirits coming from the heart [. . .] and this humor [goes] from the palate [to] the stomach and [. . .] the mesentery” (Excerpta anatomica, AT XI 599–600 [translation is mine]). Similar claims characterized Galenic tradition and also surfaced in Fernel’s work, which Descartes certainly knew, although we ignore how much he followed these texts. Yet, what appears important is to highlight the connection between the diverse parts of the body, showing a functional unity of organs. In this sense, the body is not just a sum of different pieces but also an intertwining of organs strictly connected and operating together. Yet, this connection has not just an embryological aspect. In discussing the passions, Descartes suggested an interaction between various parts of the body. For example, an interaction between the brain, the heart, and the organs of the

68

See Aucante 2000: 82–85.

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abdomen develops in the passions of love and hatred. In article 102 on love, Descartes claims that “this thought forms an impression in the brain which directs the animal spirits through the nerves of the sixth pair to the muscles surrounding the intestines and stomach, where they act in such a way that the alimentary juices flow rapidly to the heart. . .” (Passions de l’âme, art. 102, AT XI 404; CSM I 364).69 In article 103 on hatred, he affirms that “at the first thought of the object that gives rise to aversion, the spirits in the brain are so directed to the muscles of the stomach and intestines that they constrict all the openings through which the alimentary juices normally flow, thus preventing these juices from mixing with the blood. This thought also directs the spirits to the little nerves of the spleen and the lower part of the liver. . .” (Passions de l’âme, art. 103, AT XI 404–405; CSM I 364).70 Not only do the passions help clarify the mind–body composition, that is the unity of the human body, but they are also a suitable field to explore the functional unity of various organs of the body, revealing how much the animal body is a complex and coherent system of activities strictly intertwined and cohesively operating. This especially surfaces in another section of Descartes’s study of animal bodies, namely in his investigation of nutrition as a self-regulatory activity that maintains bodily proportions and balances the organs and parts of the body.71 Accordingly, selfmaintenance shows a combination of diverse activities, sensation (hunger and the recognition of suitable food), digestion, and movement of digested food in the various parts of the body through the circulatory vessels, whose combination unearths a unity of functions in keeping bodies alive. When Descartes discussed a vegetative power regulating the constitution of the body, that is, ensuring its selfmaintenance, this power cannot be restricted to the lowest organs of the abdomen or to digestion but comprehends different activities intertwined together in a functional unity.72 As a result, living bodies are not just a sum of different operations but also are a combination of such activities coherently working. As generally happens in Descartes, one should look at the opposite activity in order to have his definition of anything. In the case of life, one should thus see Descartes’s definition of death. Accordingly, aging and death occur when the body is subject to an unbalancing of parts due to the inability to self-maintain and nurture. Although the various parts continue to operate mechanically, something occurs in the body, as the functional unity is broken, and nutrition as self-maintenance of the parts ceases. This definition of death thus confirms that life consists of the harmony of different activities and various organs. As a result, animals are more a unity and coherence of activities and functions than a mechanical division of parts or the mechanical model, for the life of animals resides in their organic systems.

69

See art. 107, AT XI 408; CSM I 366. See art. 108, AT XI 408–409; CSM I 366 71 See Baldassarri 2021d: 83–85. 72 See Descartes to Regius, May 1641, AT III 372. 70

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Conclusion

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Conclusion

Similarly to the case of plants, Descartes’s study of animals discloses problems and inconsistencies. Neither a clear definition nor a history of animals surfaces in Descartes’s texts, as he was little attracted to the external diversities and mostly dealt with the internal structure and functioning of the body. This study overlaps with medicine and has no autonomy. His investigation of animals develops from his metaphysical differentiation between soul and body and the physical mechanization of nature, as he reduced animal bodies to machines. In combining anatomy and mechanics, Descartes affirmed to be able to explain all the living functions of animals. Yet, whether this resulted in a complete reduction of animals (and animal life) to machines or automata appears less clear than expected. On the one hand, neither a theoretical nor an ontological difference surfaces between animal bodies and automata (such as clocks or fountains), as Descartes notoriously began L’Homme with the hypothesis of the animal-machine. Since all bodies are mechanically framed, animals could be explained like stones, rocks, metals, and plants by means of the arrangement and combination of particles. This mechanical reduction serves his physiological investigation of the living functions. On the other hand, Descartes acknowledged the complexity of animals, attributing to them both faculties such as self-movement, sensation, emotions, memory, a form of rudimentary thought, and an internal functioning that utterly differs from inanimate bodies—and reveals a partial difference between plants and animals. What results is fascinating: The mechanical model appears as a heuristic tool that serves to explain the different functioning of the living body, while some complexities ultimately escape his mechanical reduction and must be accounted for through a systemic approach. As a tension surfaces between Descartes’s mechanical investigation of the corpuscles and the acknowledgment of higher faculties to animals, interpreters and historians have recently challenged his mechanical reductionism. In this chapter, I have moved within this tension, ultimately aiming to uncover a study of animal nature that discloses their complex behavior, while an ontological definition of animals is absent in Descartes. In his natural philosophy, the mechanical framework operates as the point of departure to understand the formation of the animal body and its operations. Isolated in themselves, each part of the animal body follows this mechanical reduction and could be expounded mechanically—this works for the heartbeat, for the stomach and digestion, for the nerves and sensation, and for instincts. For instance, the flight of birds could be explained mechanically. Yet, if taken in the complexity of the singular body, that is, in the organic coherence and unity of the body, the explanation cannot be restricted to the mechanical reduction alone, since a certain volition enters the picture. What results is that animals are not just machines. Their functioning could be mechanically expounded, while their behavior cannot—although some parts of it have a mechanical structure. For instance, machines do not grow or nurture and do not perform any internal activity, as particles do not undergo any operations within inert bodies but move, arrange, or take different shapes. In contrast, several internal activities occur in living

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bodies, revealing a mechanical complexity that is nowhere to be found in inert bodies or machines. Additionally, attributing sensation and feelings to animals entails that a form of rudimentary thought develops in them, although this is certainly different from the human mind. As a result, animal life is certainly more complex than the mechanical model and takes the shape of an organic unity that cannot be easily mechanized. In this chapter, I have focused on the challenges surfacing in Descartes’s mechanization of animal life. In the first part, I discussed the tension within his attempt to reduce the animal body to a machine, which heuristically develops as a useful model to explain the basic functions of living bodies but reveals inconsistencies in withholding sensation and the consciousness of sensation from animals. Indeed, Descartes provided animals with a mechanical form of sensation, memory, instinct, but also emotion, passion, and a very basic form of thought, as emerges in his correspondence and biomedical notes. In the second section, I explored these features within Descartes’s mechanical framework, exploring the origins of animal behaviors. Notwithstanding Descartes’s best efforts, some of these aspects cannot be reduced to his mechanical system. In the third section, I reconstructed a mechanical scale of animal bodies, from oysters to fish, birds, mammals, and finally brutes, as a gradation surfaces in Descartes’s Latin biomedical manuscripts that collected the notes reporting his anatomical dissections and observations. Descartes studied animals to understand human physiology, and some animals fit better his investigation, as some of them helped him visualize the physiology of an operation better than another, or provided him with a clearer example of a specific organic functioning. Yet, while a mechanical gradation surfaces, the boundaries between animals and humans appear more blurred. In the last section of this chapter, I presented the functional and organic unity of living bodies, as a coherence between organs surfaces at different stages of Descartes’s studies of the animal body. Differently from clocks and automata, but also from plants, animals are not just an aggregation of diverse functions or a sum of organ activities but also a coherent and organic unity of organs, as his explanation of the interaction between organs crucially highlighted. In conclusion, differently from the study of minerals, stones, rocks, and plants, in which the mechanical framework of Descartes’s physics operates without major problems or contradictions, in the case of animals, a tension persists and ultimately characterizes Descartes’s investigation. On the one hand, animals appear comparable to machines, although this only arises as a heuristic tool to ground his interpretation. On the other hand, animals present a complexity that proceeds beyond the mechanical reduction. Insofar as Descartes recognized and provided animals with higher faculties, a more complex interpretation of animal behavior surfaces, revealing that, despite everything, Descartes did not reduce life to a mere mechanical model. A fracture surfaces in Descartes’s program, for a breach distances Descartes’s metaphysics and mechanical physics from his physiology and studies of living nature, ultimately showing the difficulties in applying his philosophy to the study of natural particulars.

Chapter 7

Conclusion

On February 20, 1639, Descartes wrote to Mersenne that he had achieved a more or less satisfactory knowledge of “the animal in general [. . .] and not yet of the man in particular” (Descartes to Mersenne, February 20, 1639, AT II 526 [translation is mine]). Although he referred to this problem in the context of the possibility of treating fevers, this divide implicitly sheds light on the condition of his philosophical program, which fits the knowledge of bodies in general, but not the knowledge of particular, individual, existing bodies. In reading the whole paragraph of the letter, this point is clear. The great number and order of nerves, veins, bones, and the other parts of an animal does not demonstrate that nature is insufficient to form them, given the fact that one supposes that nature operates following the exact rules of Mechanics, dictated by God. Actually, I have considered not only what Vesalius and others had written in their Anatomy, but also several things more particular than those they wrote, which I have observed performing the dissection of several animals. This is an enterprise I have performed several times for 11 years [. . .]. But I have not found anything there, the formation of which I cannot explain in detail by means of natural causes, in the same way in which I have explained [the formation] of a grain of salt or that of a little snowflake in my Meteors. And if I was about to restart [to write] my World, where I supposed the body of an animal already formed, and where I contented myself with showing its functions, I would indicate the causes of its formation and birth. [. . .] I think I know the animal in general [. . .], but not yet the man in particular . . . (Descartes to Mersenne, February 20, 1639, AT II 526 [translation is mine])

This text contains at least two features important for us. First, Descartes confirmed that in L’Homme, he started from a supposition of the body as a statue, in which he moved from the heartbeat to explain several functions. The mechanical model operated as a hypothesis itself. Second, Descartes confirmed he had performed several more observations since L’Homme and was thus able to describe the formation of animals from the seeds, something he could not do in 1632. The difference between L’Homme and La Description du corps humain, a text elaborated in 1647–1648, resides exactly in this attention to generation, namely the explanation of the formation of living bodies from their causes, something he was unable to © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 F. Baldassarri, René Descartes’s Natural Philosophy and Particular Bodies, Studies in History and Philosophy of Science 60, https://doi.org/10.1007/978-3-031-48663-0_7

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achieve in his early works. These two points confirm that Descartes’s aprioristic reduction of nature to a geometrico-mechanical framework failed to work entirely, and he was forced to introduce suppositions and observations to guide and control deduction, and confirm his theory. He corroborates this point later in the Principia. Toward the end of this text, while summing up its contents, Descartes affirms that in his philosophy he has “considered the shapes, motions and sizes of bodies and examined the necessary results of their mutual interactions in accordance with the laws of mechanics, which are confirmed by reliable everyday experience” (Principia philosophiae, IV, art. 200, AT VIII-1 323; CSM I 286).1 Accordingly, the mathematical and mechanical reduction of nature needs to be confirmed by experimentation and observations. This is not a secondary point, as previously discussed. The unity of knowledge he envisaged through his mathematical method of the Regulae surfaces in the claim that all bodies could be accounted for from the interactions of particles of extended matter. In the letter to Mersenne, Descartes establishes that the mechanical models of his physics operate in the same way for the generation of animals and for the formation of salt or snowflakes, as a unity surfaces in the anatomical study of both inert and living bodies. In the Principia, Descartes depicts the continuity through the image of the tree of philosophy, as knowledge develops from the metaphysical roots, the principles of knowledge, the trunk of physics, the principles of nature, finally operating on cosmology and the study of terrestrial bodies, as well as on the sciences of morals, medicine, and mechanics. In this sense, the account Descartes offers of rocks, minerals, metals, plants, and animals flows from his physics and his metaphysics. Nonetheless, reducing the variety of nature to a mathematical systematization— through which he rejected any natural historical enterprise as a useless collection of diverse bodies—appropriately works for nature in general, whereas particular and individual bodies slowly dissolve. A tension thus arises, as his program of reducing nature to his metaphysical physics remains incomplete. In the Principia, after having laid bare the principles of his philosophy, Descartes unfolds his study of nature from a short history of all natural phenomena—something he had previously demanded— in order to corroborate his investigation of nature and particular bodies. By means of the latter, he affirmed that he was able to account for the whole of nature in the mechanical terms of his physics. In this book, I have dealt with the problems of the dissolution of particular bodies within his philosophical enterprise, rooted in his metaphysical physics according to which nature is a geometrical combination of particles extended in figures, sizes, and shapes. In the Discours, Descartes appeared optimistic concerning the possibility of his method to expound all bodies, especially rocks, minerals, metals, plants, and animals in a way that is consistent with his philosophical program.2 But this method

1 Original Latin is: “Nempe figuras et motus et magnitudines corporum consideravi, atque secundum leges Mechanicae, certis et quotidianis experimentis confirmatas.” 2 Discours de la Méthode, VI, AT VI 43–44; CSM I 133.

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reflects little of the extreme rationalism of the Regulae. Later on, in a letter to Mersenne, Descartes claimed that his principles apply to all bodies, allowing him to explain all living nature, for instance.3 Notwithstanding Descartes’s best efforts, bridging the gap between his metaphysics and physics with his natural philosophy (and natural history intended as the knowledge of particular bodies) remains partial. In the introduction, I discussed this fracture, while in the chapters of this book I have focused on the ways he dealt with these problems. For instance, as examined in Chap. 2, the transformations from the epistemology of the Regulae, grounded on intellectual operations and on an a priori system of knowledge and on the rejection of experience and probable conjecture, and his later epistemological practice. In the Discours and the Principia, Descartes opened out to a posteriori knowledge, experimentation, hypotheses, and suppositions. A similar change arises in Descartes’s interpretation of nature, as examined in Chap. 3. Although his definition of nature as extended matter persisted through his philosophical career, and significantly shaped his physics, the study of nature in Le Monde differs from the natural historical reconstruction of the Principia, as he recognized the necessity to treat particular bodies or phenomena from a more empirical perspective. These two aspects run somehow parallel in Descartes’s program, as his philosophy mostly consisted in the attempt to reduce the knowledge of nature to a rationalistic framework—ultimately replacing Aristotelian physics in the schools. Yet, Descartes’s engagement with particular bodies significantly benefitted from experiments and observations he had performed through the time. In the second part of the book, I explored Descartes’s investigations of particular bodies in detail. In Chap. 4, I investigated inert bodies such as rocks, stones, minerals, and metals; in Chap. 5, I analyzed plants, and in Chap. 6, I explored Descartes’s studies of animals. In focusing on these bodies, differences emerge in Descartes’s philosophy. He applied his method in all these disciplines and reduced their objects to his mechanical physics, fleshing out a philosophy of nature consistent with the principles of his metaphysics and physics. In this sense, through performing experiments and observations, Descartes applied the theory of his mechanical physics to particular natures. However, differences surface too. While his method suitably operates for the case of rocks, minerals, and metals, which he reduced to the mechanical laws of his physics—albeit only following an a posteriori reasoning—problems arise with living bodies, plants and animals. A mechanical gradation between bodies results, as I highlighted in Chaps. 5 and 6— therefore revealing the different mechanical complexities of bodies and the restrictions or impossibilities in mechanizing them. In the study of animals, Descartes did not merely focus on their mechanical activities but accounted for their system, that is, for the unity and coherence of the animal body, proceeding beyond the mere mechanization of their parts, as it was for minerals and plants. Animal life is a coherent organization of functions, albeit not as a mere abstract machine. Also, plants reveal some challenges, as they do not entirely overlap with automata (or inert

3

Descartes to Mersenne, July 30, 1640, AT III 122.

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bodies in general), despite Descartes’s 1637 claim analyzed in Chap. 5. In this case, Descartes’s philosophy provided botany with a more autonomous status, anticipating the innovative features of seventeenth-century botanical studies. As a result, while facing the difficulties of observing the nature of diverse, particular bodies, Descartes’s commitment to his metaphysical physics was seriously undermined. Balancing between a metaphysical ground and a more experiential approach to nature ultimately shaped early modern philosophy, opening a breach with those Cartesian proponents who engaged with nature. In this book, I have highlighted how much this balance especially surfaces in Descartes’s correspondence and unpublished texts, while he dealt with particular bodies, ultimately showing his varied attempt to provide a complete mechanization of nature consistent with his program—although much of his early strict and rationalistic epistemology was lost through the years. In working on particular bodies—from the Bologna stones and the sensitive herb to salt, magnets, flight of birds, as well as cows and sheep, just to name a few cases collected in this book— Descartes took full advantage of the malleability of his method, applying the mathematical reasoning and the mechanical reduction of nature a posteriori, since an a priori order was not always attainable. In this way, a mechanization of inert and living bodies resulted, and a complete picture of nature in mechanistic terms was possible. Still, difficulties in bridging the gap between his metaphysics and physics and his natural philosophy emerges, and the study of particular bodies reveals a tortuous path from the roots of the tree to its branches, substantially marking Descartes’s philosophical program entirely.

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Index

A Aldrovandi, U., 8 Aquapendente, H.F. ab, 171 Ariew, R., 6, 11, 20, 52 Armogathe, J.-R., 11, 12, 68 Arriaga, R. de, 123 Aucante, V., 12, 38, 138, 140, 141, 154, 166, 168, 169, 181

B Bacon, F. Baconian, 2, 39, 41, 127, 131, 132, 134, 135, 137, 150 Baillet, A., 75, 76, 156 Bauhin, C., 129 Beeckman, I., 5, 16, 19, 22, 34–36, 68, 69, 90, 91, 104, 105, 127–130, 132, 143 Belgioioso, G., 11, 12, 173, 177 Bodin, J., 9 Bonicalzi, F., 4, 154, 158 Bos, E.-J., 30, 41, 80, 164 Brosterhuysen, J. van, 127, 130–132, 134

C Cabeo, N., 87, 106 Cardano, G., 8 Carraud, V., 33, 60–62 Casciarolo, V., 87 Cavendish, W. (Marques of Newcastle), 81, 97, 101, 160, 170, 175, 177 Cesalpino, A., 121 Chandoux, N. de Villiers, 75, 76, 79

Charron, P., 160 Clarke, D., 6, 29, 30, 41, 43, 118 Clerselier, C., 177 Clusius, C., 8, 127 Colvius, A., 87 Costeo, G., 121 Cottingham, J., 157

D De Buzon, F., 14, 22, 26, 46, 60–62 Della Porta, G., 103, 137, 146 Des Chene, D., 4, 123, 125, 138, 142, 155, 178, 179 De Wilhem, David le Leu, 80, 131, 135, 136 Dibon, P., 128, 132, 135 Dika, T., 6, 19, 20, 23, 25, 28, 31, 36 Dodoens, R., 127 Du Val, D., 121

E Elisabeth of Bohemia, Princess, 97, 103, 104

F Fernel, J., 181 Fromondus Libertus (Libert Froidmont), 93

G Gabbey, A., 4, 59, 118 Galilei, G., 104

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 F. Baldassarri, René Descartes’s Natural Philosophy and Particular Bodies, Studies in History and Philosophy of Science 60, https://doi.org/10.1007/978-3-031-48663-0

207

208 Garber, D., 4, 6, 11, 21, 26, 30, 32, 43–48, 52, 59, 68, 121, 161, 169 Gassendi, P., 2, 3, 104, 122, 138 Gaukroger, S., 10, 11, 15, 24, 34, 46, 57, 62, 75, 76, 118, 120, 126, 154, 159, 161 Gessner, C., 8 Gilbert, W., 104–107, 115 Golius, J., 90 Gouhier, H., 147 Grandamy, J., 108, 109

H Habernfeld, Andreas of [Mercurius Cosmopolita], 80 Harrison, P., 157 Hatfield, G., 30, 154, 157, 161, 166 Hattab, H., 6, 11, 32, 54, 59, 91, 93, 95 Hogelande, C. van, 23, 39 Huygens, C., 39, 41, 80, 84, 85, 96, 104, 108, 109, 115, 120, 127, 130–134 Hyperaspiste, 87

J Joly, B., 12, 75, 76, 78, 79, 85, 92, 96, 97, 99, 102, 103

K Kepler, J., 2, 36 Kircher, A., 77, 107, 108, 118, 119

L Leibniz, G.W., 125, 140, 142 Liceti, F., 87 Lobel, M. de, 127 Lojacono, E., 9, 27, 39, 41, 48, 68, 71

M Marion, J.-L., 6, 27, 30 Mehl, E., 12, 15, 52, 79 Mersenne, M., 2, 3, 5, 9, 16, 34, 37–41, 51, 53, 56, 57, 64, 66, 68, 75, 77, 79–88, 90, 91, 94, 95, 103–109, 114, 118, 125, 126, 129, 133–135, 146, 153, 154, 160, 162– 168, 171, 173, 174, 179, 180, 185–187 Meyssonnier, L., 80, 81, 83 Montaigne, M. de, 160

Index Morin, J.-B., 45, 46, 75

P Peiresc, N.-C.F. de, 8, 9, 40 Plato, 21, 23 Plempius, V.F., 4, 66, 67, 93, 101, 141, 153 Pollot, A., 66, 94, 124, 159, 162 Popkin, R., 76

R Regius, H., 95, 111, 117, 124, 126, 164, 174–176, 182 Reneri, H., 3, 41, 66, 94, 124, 127, 134–137, 140, 150, 159, 162 Rodis-Lewis, G., 14, 75, 118, 158 Roux, S., 4, 59, 80 Ruler, H. van, 2, 9

S Scheiner, C., 3 Schook, M., 117 Schuster, J., 4, 11, 34, 52, 64, 106, 110 Schuyl, F., 176 Sennert, D., 137 Shapiro, L., 34, 103 Smetius, S., 104, 105 Stelluti, F., 86 Straten, S. van der, 84, 85 Suarez, F., 54

T Taegio, B., 146 Tidike, F., 121 Trevisani, F., 80, 174

V Van Berkel, K., 22, 34, 104, 105, 130 Van Beverwijck, J., 174 Van Zurck, A.S., 133 Vatier, A., 20, 44, 45 Verbeek, T., 13, 27, 30–32, 37, 41, 53, 56, 75, 90, 95, 105, 108, 127, 133, 135, 154 Villebressieu, E., 59, 75, 76, 79, 82 Villiers, C., 75, 80, 81, 83 Voetius, G., 95, 117, 118 Vorstius, A., 133